35 U.S.C. 301 Citation of prior art.

Any person at any time may cite to the Office in writing prior art consisting of patents or printed publications which that person believes to have a bearing on the patentability of any claim of a particular patent. If the person explains in writing the pertinency and manner of applying such prior art to at least one claim of the patent, the citation of such prior art and the explanation thereof will become a part of the official file of the patent. At the written request of the person citing the prior art, his or her identity will be excluded from the patent file and kept confidential.

37 C.F.R. 1.501 Citation of prior art in patent files.

1. (a) At any time during the period of enforceability of a patent, any person may cite, to the Office in writing, prior art consisting of patents or printed publications which that person states to be pertinent and applicable to the patent and believes to have a bearing on the patentability of any claim of the patent. If the citation is made by the patent owner, the explanation of pertinency and applicability may include an explanation of how the claims differ from the prior art. Such citations shall be entered in the patent file except as set forth in §§ 1.502 and 1.902.
2. (b) If the person making the citation wishes his or her identity to be excluded from the patent file and kept confidential, the citation papers must be submitted without any identification of the person making the submission.
3. (c) Citation of patents or printed publications by the public in patent files should either: (1) Reflect that a copy of the same has been mailed to the patent owner at the address as provided for in § 1.33 (c); or in the event service is not possible (2) Be filed with the Office in duplicate.

37 C.F.R. 1.502 Processing of prior art citations during an ex parte reexamination proceeding.

Citations by the patent owner under § 1.555 and by an ex parte reexamination requester under either § 1.510 or § 1.535 will be entered in the reexamination file during a reexamination proceeding. The entry in the patent file of citations submitted after the date of an order to reexamine pursuant to § 1.525 by persons other than the patent owner, or an ex parte reexamination requester under either § 1.510 or § 1.535, will be delayed until the reexamination proceeding has been terminated. See § 1.902 for processing of prior art citations in patent and reexamination files during an inter partes reexamination proceeding filed under § 1.913.

37 C.F.R. 1.902

Citations by the patent owner in accordance with § 1.933 and by an inter partes reexamination third party requester under § 1.915 or § 1.948 will be entered in the inter partes reexamination file. The entry in the patent file of other citations submitted after the date of an order for reexamination pursuant to § 1.931 by persons other than the patent owner, or the third party requester under either § 1.915 or § 1.948, will be delayed until the inter partes reexamination proceeding has been terminated. See § 1.502 for processing of prior art citations in patent and reexamination files during an ex parte reexamination proceeding filed under § 1.510.

Prior art in the form of patents or printed publications may be cited to the Office for placement into the patent files. Such citations may be made without payment of a fee. Citations of prior art may be made separate from and without a request for reexamination.

The basic purpose for citing prior art in patent files is to inform the patent owner and the public in general that such patents or printed publications are in existence and should be considered when evaluating the validity of the patent claims. Placement of citations in the patent file along with copies of the cited prior art will also ensure consideration thereof during any subsequent reissue or reexamination proceeding.

The citation of prior art provisions of 35 U.S.C. 301 and 37 CFR 1.501 do not apply to citations or protests filed in pending applications.