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903 Classification in USPC [R-07.2015]

903.01 Statutory Authority [R-08.2012]

The statutory authority for establishing and maintaining a classification system is given in the following statute, which states:

35 U.S.C. 8   Classification of patents.

The Director may revise and maintain the classification by subject matter of United States letters patent, and such other patents and printed publications as may be necessary or practicable, for the purpose of determining with readiness and accuracy the novelty of inventions for which applications for patent are filed.

903.02 Basis and Principles of Classification [R-10.2019]

Many of the principles that form the basis of classification used in the U.S. Patent and Trademark Office are set forth in the "Examiner Handbook to the U.S. Patent Classification System" which can be accessed from either the intranet on the Classification Home Page ( classification-resources/) or the internet on the Office of Patent Classification home page ( classification-standards-and-development). Any questions not covered in this handbook can be directed to the Office of Patent Classification.

903.02(a) [Reserved]

903.02(b) Scope of a Class in the USPC [R-07.2015]

In using any classification system, it is necessary to analyze the organization of the class or classes to be included in the search.

The initial analysis should determine which one or ones of the several types of subject matter (manufacture, art, apparatus, or stock material) are contained in the class being considered.

Further, relative to each type of subject matter, it is necessary to consider each of the various combinations and subcombinations set out below:

Basic Subject Matter Combined with Feature for Some Additional Purpose. The added purpose is in excess of the scope of the subject matter for the class, as defined in the class definition; e.g., adding a sifter to a stone crusher which gives the added function of separating the crushed stone.

Basic Subject Matter Combined with Perfecting Feature. Features may be added to the basic subject matter which do not change the character thereof, but do perfect it for its intended purpose; e.g., an overload release means tends to perfect a stonecrusher by providing means to stop it on overload and thus prevent ruining the machine. However, this perfecting combined feature adds nothing to the basic character of the machine.

Basic Subject Matter. The combination of features necessary and essential to the fundamental character of the subject matter treated; e.g., a stonecrusher requires a minimum number of features as essential before it can function as such.

Subcombinations Specialized to Basic Subject Matter. Each type of basic subject matter may have subcombinations specialized to use therewith; e.g., the crushing element of a stonecrusher.

Subcombinations of General Utility. Each type of basic subject matter may have subcombinations which have utility with other and different types of subject matter; e.g., the machine elements of a stonecrusher. Subcombinations of this character usually are provided for in some general class so that the examiner should determine in each instance where they are classified.

903.03 Availability of Foreign Patents [R-07.2015]

Many foreign patent documents received in the Office before October 1, 1995 were placed in the shoes in the Technology Center (TCs), according to either the United States Patent Classification System (USPC) or, in relatively few instances, the International Patent Classification (IPC) system. Foreign patents received by the Office after October 1, 1995 are available on the USPTO’s automated search systems, the Foreign Patent Access System (FPAS), Internet sites, and the Scientific and Technical Information Center (STIC) collections.

If the examiner desires to update the classification of a foreign patent by changing, canceling, or adding copies, he or she should forward the patent (or bibliographic information) to his or her supervisory patent classifier with a request for the desired transaction attached.

The Foreign Patents Service Center manages Main STIC. STIC’s collections are international in scope and include foreign patents, non-patent literature, designs, trademarks, and legal information. There is an assortment of resources which reflect the information needs of examiners and researchers working in various fields of science and technology. The staff is experienced in foreign patent data retrieval, patent family searches, and document retrieval services for non-patent literature in the STIC collections.

Examiners confronted with language problems in classifying foreign-language patents may call upon the Translations Service Center of STIC for assistance (see MPEP § 901.06(a)). In addition, the Translations Service Center retains copies of translated foreign patents in the database.

903.04 Classifying Applications for Publication as a Patent Application Publication in USPC [R-07.2015]

Patent applications filed on or after November 29, 2000, are published as a patent application publication pursuant to 35 U.S.C. 122(b), unless certain exceptions apply. See MPEP § 1120.

Patent application publications are given a primary classification (equivalent to an original classification), and may also be given a secondary classification (equivalent to a cross reference). While there may be only one primary classification for a single patent application publication, there may be any number of secondary classifications. The selection of a primary classification of a patent application publication is based on the application’s main inventive concept using the claims as a guide. A primary classification could be any U.S. class/subclass (except cross reference art collections, digests and foreign art collection subclasses). A secondary classification is based on other inventive concepts (mandatory) or valuable disclosure (discretionary), and may be any U.S. class/subclass (including cross reference collections and digests, but excluding foreign art collection subclasses). The classification of a patent application publication is printed on the front page of the publication.

At least 9 weeks prior to the projected publication date, applications are classified using programs designed to enable entry of certain data required for publication of patent applications. Applications are classified by giving each application at least a primary classification and an international classification. The suggested international classification(s) corresponding to each assigned U.S. classification is provided. In addition, if a figure is to be published, the figure is selected at the time of classification.

903.05 Addition, Deletion, or Transfer of U.S. Patents and U.S. Patent Application Publications [R-08.2012]

Requests for addition, deletion, or transfer of official copies of U.S. patents and U.S. patent application publications may be carried out by using the Patent Post Publication Classification Manager and the PGPub Post Publication Classification Manager, which are available online from the Classification Home Page under the heading Patents, their Classifications and Locations. The Classification Home Page is accessible from the desktop via the Patent Examiner’s Toolkit.

Using these tools, examiners can request the following transactions:

  • (A) Add any classification(s) from the U.S. Patent Classification system as a cross-reference (XR) classification to a patent or a secondary classification to a patent application publication.
  • (B) Delete XR classification(s) or secondary classification assigned to the Technology Center (TC) of the person requesting the deletion.
  • (C) Change original classifications (ORs) or primary patent application publication classification to a classification in the TC of the person requesting the change.
  • (D) Add or delete any International Patent Classification system (IPC) classification to a patent.

903.06 Harmonized Subclasses [R-07.2015]

The U.S. Patent Classification System (USPC) includes subclasses that have been harmonized with subclasses from the European Patent Office (EPO) and the Japan Patent Office (JPO). Subclasses that have been harmonized have a designation of "EPO," "JPO," or "EPO/JPO" in parentheses following the subclass title to indicate if the subclass has been harmonized with the EPO or JPO or with both systems.

903.07 Classifying and Cross-Referencing at Allowance [R-10.2019]

When an application is passed to issue, it is the duty of each primary examiner to personally review the original classification and cross-referencing made by his or her assistants in the issuing classification boxes on the Image File Wrapper (IFW) issue classification form. This form provides space for the full name of the "Primary Examiner" to show that the review has been made. An examiner with full signatory authority who acts personally on an application and sends it to issue should stamp and sign his or her name on the IFW issue classification form ONLY in the "Primary Examiner" space.

An application, properly classified at the start of examination, may be classified differently when it is ready for allowance. The allowed claims should be reviewed in order to determine the subject matter covered thereby. It is the disclosed subject matter covered by the allowed claims that determines the original and any mandatory cross-reference classification of U.S. patents.

The procedure for determining the classification of an issuing application is as follows: every claim, whether independent or dependent, must be considered separately for classification. A separate mandatory classification is required for each claim which is classifiable in a different class or subclass; some claims, particularly in chemical areas, may require plural classifications. After all mandatory classifications have been determined, the classification to be designated as the original (OR) is determined. If all mandatory classifications are in the same class, the original classification is the mandatory classification that, looking at the schedule from the top down, is the most indented subclass array in which any classifications are assigned, in certain circumstances (e.g., the genus-species array), however, modifications of this rule may apply. See the "Examiner Handbook to the U.S. Patent Classification System" for an explanation of genus-species classification.

If the mandatory classifications are in different classes, the original classification is determined by considering, in turn, the following criteria:

  • (A) selection based on the most comprehensive claim,
  • (B) selection based on priority of statutory category of invention,
  • (C) selection based on superiority of types of subject matter, and
  • (D) selection among classes in the "related subject" listing at the front of the manual of classification.

It should be noted that the criteria, supra, may be superseded by

  • (A) special circumstances, e.g., superconductor technology and biotechnology are superior to all other subject matter,
  • (B) prior placement of patents for a particular body of art, or
  • (C) particular class lines and class notes.

Once the controlling class is determined, the original classification, looking at the schedule from the top down, is the mandatory classification that is the most indented subclass of the first subclass array in which any classifications are assigned.

For a more complete discussion of this subject, see the "Examiner Handbook to Classification" which is available online to USPTO personnel from the Classification Home Page under the heading "General Training". The Classification Home Page ( is accessible from the desktop via the Patent Examiner’s Toolkit.

Once the original classification is determined, all remaining mandatory classifications are designated as cross-references, as are any additional discretionary classifications that the examiner wishes to apply to the patent.

The examiner must complete the IFW issue classification form to indicate the class and subclass in which the patent should be classified as an original and also the classifications in which it should appear as a cross-reference. The examiner should be certain that all subclasses into which cross-references are placed are still valid.

All examiners must include alpha subclass designators in the issuing classification boxes on the IFW issue classification form at the time of issue when appropriate. This applies to both the original classification and the cross-reference classification. Any time that a patent is being issued in or cross-referenced to a subclass containing alpha subclasses, the alpha designation for the proper alpha subclass must be included. No other designation is permissible. Inclusion of only the numeric designation of a subclass which includes an alpha subclass designation is an incomplete and improper entry. A numeric subclass from which alpha subclasses have been created is designated with an "R" (denoting residual), and if the patent does not fit an indented alpha subclass, the "R" designation must be included. It is permissible to place multiple copies of a patent into a single set of alpha subclasses.

Digests and cross-reference art collections should also be included in the issuing classification boxes on the IFW issue classification form, but the original classification must never be a digest or cross-reference art collection. The indication for a copy of a patent in a digest or cross-reference art collection must be in the cross-reference area of the issuing classification boxes. A digest must be identified by class number, alpha characters DIG, and appropriate digest number.

U.S. patents cannot be classified in subclasses beginning with "FOR," since these are exclusively for foreign patents.


Where an official classification order affects an application already passed to issue, the Office of Patent Classification oversees any necessary changes. Patents issuing from applications which already have been sent to the printer will be reclassified.

903.07(a) Cross-Referencing — Keep Systematic Notes During Prosecution [R-08.2012]

Throughout the examination of an application, systematic notes should be kept as to cross-references needed either due to claimed or unclaimed disclosure. Examiners handling related subject matter should be consulted during prosecution (whether they handle larger unclaimed combinations or claimed or unclaimed, but disclosed, subcombinations), and asked if cross-references are needed.

Each consultation involving a question of the propriety of the classification of subject matter and/or the need for a cross-reference must be recorded in the SEARCH NOTES box on the file wrapper and must include: the name of each examiner consulted, the date that the consultation took place, and the results of the consultation including the consulted examiners’ or examiner’s indication of where claimed subject matter is properly classified and where subject matter disclosed but unclaimed is properly classified and whether or not a cross-reference is needed.

A cross-reference MUST be provided for all CLAIMED disclosure where possible and inserted in the issuing classification boxes at time of issue.

903.08 Applications: Assignment and Transfer [R-07.2015]

The titles "supervisory patent examiner" and "primary examiner," as used in this Chapter 900, include in their definition any person designated by them to act on their behalf. It is recognized that authority to accept or refuse the transfer of an application may be delegated when such authority is deserved.

The Technology Center (TC) to which an application is assigned is responsible for its examination until such time as the application is officially transferred to another TC.

The primary examiners have full authority to accept any application submitted to them that they believe is properly classifiable in a class in their art unit.

903.08(a) New Applications [R-07.2015]

New nonprovisional applications are assigned to the various Technology Centers (TCs) in the first instance by the Office of Patent Application Processing (OPAP).

When a new application is received which, in the opinion of the primary examiner, does not belong to his or her TC, he or she may request transfer of it to another TC. See MPEP § 903.08(d).

If the search in connection with the first action develops art showing proper classification elsewhere, the transfer is usually initiated before the first action is prepared and mailed.

903.08(b) Classification and Assignment to Examiner [R-07.2015]

Every nonprovisional application, new or amended, and including the drawings, if any, when first assigned to a Technology Center (TC) must be classified and assigned to an examiner for examination. The supervisory patent examiner normally assigns the application to an examiner. Provisional applications are not classified or assigned since they are not examined.

If an examiner other than the supervisory patent examiner is given the responsibility of assigning applications, time so spent may, at the TC Director’s discretion, be charged to "Assisting SPE."

903.08(c) Immediate Inspection of Amendments [R-08.2012]

Upon the receipt of an amendment which makes a transfer proper, steps should be taken promptly in accordance with the transfer procedure outlined in MPEP § 903.08(d).

903.08(d) Transfer Procedure [R-10.2019]


Each Technology Center (TC) has developed internal procedures for transferring application between art units and resolving application assignment disputes.


Where a supervisory patent examiner (SPE) believes an application, either new or amended, does not belong in their art unit, they may request transfer of the application from their art unit (the "originating" art unit) to another art unit of a different TC (the "receiving" art unit).

The decision as to the classification resolution and assignment of an application is made by agreement between the SPEs involved in the transfer. If no agreement can be reached between the SPEs, the application may be forwarded to the classification dispute TC representative panel of the TC where the application was originally assigned for a final decision. The classification dispute TC representative panel consists of designated representatives from each TC.

Before an application is sent to a receiving art unit of a different TC, the application must be fully reviewed to ensure that all appropriate areas in the originating TC have been considered with respect to the classification of the application. In all cases when a transfer is initiated, the application must be sent on transfer inquiry to a receiving art unit. Even if the application is confusing or contains unfamiliar subject matter, the SPE of the originating art unit must make his or her best judgment as to where the application should be classified and attempt to transfer it there.

Where an application’s claims include a combination of limitations for plural disciplines (chemical, electrical, or mechanical), an SPE or primary examiner may request transfer to another discipline, notwithstanding the fact that the controlling claims are properly classified in his or her art unit, on the ground that the application is "best examinable" in the other discipline. In this instance, the SPE or primary examiner requesting transfer should cite art showing the limitations classifiable in his or her discipline. For discussion of the situations in which assignment of an application on a "best examinable" basis may be proper, see MPEP § 903.08(e).


When the SPE or primary examiner of the originating art unit determines that a transfer is appropriate, they must initiate a request through the Patent Transfer Inquiry (PTI) system ( and provide a full explanation of the reasons for classification in the receiving art unit. At least one of the following should be included in the form in the space provided:

  • (A) Identification of the controlling claim;
  • (B) Identification of any existing informal transfer agreement; or
  • (C) Other reasons – with full explanation.

If the SPE or examiner of the originating art unit believes an application has been improperly assigned to their art unit, but is unable to determine an appropriate place to send the application, a "gatekeeper" or search assistant should be consulted. A listing of examiners who function in this role may be found at http://ptoweb/patents/tsa/. It is noted that "gatekeepers" or search assistants exist in all of the TCs except the TC that examines design applications (TC 2900).

If the receiving SPE or primary examiner agrees to accept the application, they classify and assign the application. The transfer is effected by accepting the application in PTI.

If the receiving SPE or primary examiner refuses to accept the application, the reasons for refusal must be entered in PTI. The refusal must be recorded in PTI. Where the application is an application (other than a PCT application) that has not been docketed to an examiner, the originating art unit may then either accept the application for examination or send the disputed transfer application to the classification dispute TC representative panel for final resolution. The panel considers the statements and evidence of both the originating and receiving art units and assigns the application to the art unit that has jurisdiction over the art in which the controlling claims of the application are properly classified.

Under certain circumstances, the classification dispute TC representative panel, contrary to controlling classification rules, may assign an application to a class or art unit which the panel deems is better equipped to examine the application. See MPEP § 903.08(e).

Every application, no matter how peculiar or confusing, must be assigned somewhere for examination. Thus, in contesting the assignment of an application, the SPE or primary examiner should indicate another class that is a better class in which to classify the application, rather than simply arguing that the application does not fit the examiner’s class.

If an application contains both classification issues and issues unrelated to classification, e.g., a dispute both as to the classification of claims and the propriety of restriction, the issues unrelated to classification should be resolved first. If, thereafter, classification issues still need to be addressed, application transfer may be appropriate. For the procedure in the classification groups for applications which contain examining corps issues, see MPEP § 903.08(e).

The question of need for a restriction requirement does not influence the determination of transfer.

If an application has been assigned a class/subclass by the Office of Patent Application Processing (OPAP) and the application is routed to an art unit that does not examine applications assigned to that class/subclass, an IFW message to the "OIPEClass/GAUMismatch" IFW mailbox should be sent.

903.08(e) General Guidelines Governing the Assignment of Nonprovisional Applications for Examination [R-10.2019]

This section applies only to nonprovisional applications. It does not apply to provisional applications since such applications are not examined.

The following are only general guides, and exceptions frequently arise because of some unusual condition. Patent examiners are confronted with an already existing classification made up of newly revised classes, those revised years ago and which have somewhat outgrown their definitions and limits, and still others made a generation ago and never changed. Also, these classes are based on different theories and plans, some on art, some on structure, some on functions, and some on the material worked upon. The patent examiners cannot change this existing condition as each application comes up for assignment, but must seek to place the cases where they are appropriately assigned. An application will be assigned as follows:

  • (A) The assignment of nonprovisional applications follows, as far as possible, the rules or principles governing the classification of patents. Applications are generally assigned on the basis of where the application would have an original classification, if the claims it contains were in a patent.
  • (B) The criteria by which the original classification is determined are set forth in MPEP § 903.07.
  • (C) The claims and statement of invention are generally taken as they read; however, claims must be read in light of the disclosure (claimed disclosure). Any attempt to go behind the record and decide the case upon what is deemed the "real invention" would, it is believed, introduce more errors than such action would cure. Supervisory patent examiners (SPEs) cannot possess the specific knowledge of the state of the art in all the classes that the patent examiners collectively possess. Further, such questions are matters of merit for the examiners to determine and are often open to argument and are subject for appeal.
  • (D) Within a class, looking down from the top of the schedule, the OR subclass is chosen from among the classifications of the claimed disclosure according to whichever one is the most indented subclass of the first subclass array.
  • (E) As stated in MPEP § 903.07, the location of the United States patents constituting the prior art is generally controlling over all else. (Note: Where time permits, obvious misplacements of the patents constituting the prior art are corrected, but to straighten all lines as the cases come up for assignment would require the time of several people.)
  • (F) Ordinarily, an application cannot be assigned to a class which includes one element or part only of several claimed in combination. The claim is treated in its entirety.
  • (G) The classification dispute TC representative panel is authorized in all cases, where they evaluate the facts as warranting it, to assign applications for examination to the TC best able to examine the same. Since assignment for examination on this basis will at times be contrary to classification of patents containing the same character of claims, the classification dispute TC representative panel will indicate the proper classification of the patent, if such claims are allowed.
    • Thus, in cases where there is a claim drawn to hybrid or mixed subject matter and the SPE in one discipline determines that the application requires consideration by, or may be best examined by, a TC in one of the other technical disciplines, chemical, electrical, or mechanical, he or she may request a transfer of the application on a "best examinable" basis, in accordance with this subsection.
    • Some examples of applications which may be thus submitted include the following:
    • (1) An application containing a hybrid claim wherein, for instance, a product is defined merely in terms of the process for producing it. See MPEP § 705.01(e), situation (A).
    • (2) Where an application properly assigned to a mechanical or electrical class contains at least one claim to mixed subject matter, a part of which is chemical, the application may be assigned to the appropriate chemical art unit for examination; or where the application is properly assigned to a mechanical class and a claim therein contains electrical subject matter, the application may be assigned to the appropriate electrical art unit for examination.

    As indicated earlier, when an application which had been assigned for examination in accordance with this subsection ultimately is allowed, it will be classified according to the controlling claim. In effect, assignment for examination may be on a "best examinable" basis, but the patent will issue and be classified according to the rules of superiority in classification; thus, the search file will have a constant set of rules governing placement of patents therein.

    Where an application is being reassigned from one examining discipline to another, under the provisions of the "best examinable" practice, the person requesting the transfer is ordinarily required to cite references pertinent to the claimed features falling under the jurisdiction of the art within his or her discipline. In those cases wherein the application of the reference(s) is not evident or clear, the transferring examiner should include a brief statement explaining the relation and possible application of the reference(s) to the claim(s); in case of dispute as to the necessity of this procedure, the classification dispute TC representative panel has power to require the statement.

  • (H) When an application has been taken up by an examiner for action and a requirement to restrict is found necessary, a part of the claims being directed to matter classifiable in the TC where the case is being examined, an action requiring restriction should be made without seeking a transfer of the case to another TC. The action of the applicant in reply to the requirement for restriction may result in making a transfer of the application unnecessary.
  • (I) Ordinarily, where all the claims of an application are for an article made of a specific composition or alloy with no other structure of the article recited, the application will be assigned to the composition or alloy class.
  • (J) A class of cases exists in which either no art or a divided art is found and in which no rule or principle is involved. Such cases are placed where, in the judgment of the classification TC representative panel, they will be best searched and adjudicated. It is often impossible to so explain a decision in this class of cases as to satisfy, or in any way aid, the examiners interested. Indeed, the reasons for or against sending such cases one place or another may be so evenly balanced that no reason of any value can be given.
  • (K) An examiner seeking the transfer of a case may make a search, both of his or her own class and the class to which he or she thinks the case should be transferred, and the examiner in charge of the art unit should ensure the record includes the result of the search.
  • (L) When an application is received by the classification dispute TC representative panel in which there is a matter under dispute which is not related to the classification of a claim but which is in the purview of the TCs, e.g., propriety of a restriction requirement, timeliness of submission for transfer, etc., as well as a dispute over the classification of claims, the application will be returned to the originating TC for resolution on the issues unrelated to the classification.

It is important that newly received applications be immediately screened for these situations so that, if necessary, the applications may be promptly returned to the originating TC.

If after resolution of the issues unrelated to the classification, there is still a dispute as to which TC should examine the application, the originating application may be returned to the classification dispute TC representative panel for assignment.


The flowchart below shows the routing of an application between TCs. (For routing of applications between art units within the same TC, see MPEP § 903.08(d).) The application should be considered by the receiving art unit in the TC (TC1), which will accept the application and assign it to an examiner, or forward it to an art unit in another TC (TC2) for consideration. An art unit in TC2 will classify and assign the application to an examiner, return the application to the SPE of the originating art unit, or forward it to an art unit in another TC (TC3). If the art unit in TC2 is not aware of any other likely classification, the application may be returned directly to the SPE of the originating art unit in TC1. In any of these scenarios, the decisions concerning the transfer must be recorded in the Patent Transfer Inquiry (PTI) system.

Where the application is forwarded to an art unit in TC3 and the art unit in TC3 declines to accept the application, the application should be returned to the SPE of the originating art unit in TC1.

If an art unit in TC2 or TC3 declines to accept the application and the application is returned to the SPE of the originating art unit in TC1, the SPE of the art unit in TC1 may forward the application to a classification dispute TC representative panel for resolution. The SPE of the art unit in TC1 may contact a TC classification panel representative within his or her TC. The application will be given to the TC classification panel representative and the representative will contact either the TC2 or TC3 representative (forming a classification dispute TC representative panel) to set up a conference. The classification dispute TC representative panel will evaluate any evidence presented by the disputing TCs, and make a decision on the proper classification and assignment of the application. The decision of the classification dispute TC representative panel will be final and binding.

Inter-TC Classification Dispute Resolution Procedures


SPEs and examiners must use the Patent Transfer Inquiry (PTI) system, which creates a record of the transfer inquiry history of each application and facilitates tracking of applications.

903.09 [Reserved]

903.09(a) [Reserved]



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Last Modified: 06/25/2020 18:23:21