Under U.S. patent law, an invention lacks novelty if it was described in a U.S. patent granted on an application by another that was filed in the U.S. prior to the date it was invented by the applicant for a patent. [35 U.S.C. 102(e)]. This issue usually arises when one or more applicants file a second U.S. patent application that claims an invention that was described in a earlier-filed patent application that was filed by a different "inventive entity." The inventive entities of two applications are different if not all the inventors are the same. The applicant(s) filing of the second application may occur during the pendancy of the earlier-filed U.S. patent application or after it issues as a patent.
This rule is a special case in that the document (called a "reference") that destroys novelty becomes "effective" (has an effective date that occurs) when the reference is still unpublished (because not all U.S. applications are published). If the applications are both assigned to the same entity or if there is any overlap in inventorship (there is at least one common inventor who is listed in both applications), the issue can even arise before the earlier-filed application issues.
When a U.S. patent application filed prior to November 29, 2000, which has not been voluntarily published by the USPTO is being examined, only issued U.S. patents and issued Statutory Invention Registrations can destroy novelty under this rule; issued non-U.S. (foreign) patents cannot. However, as was noted above, if there is common owership or inventorship, maintaining the secrecy of the earlier-filed application is not an issue, and a "provisional" rejection of the later-filed application can be made under 35 U.S.C. 102(e). Anything that could have been claimed in the reference can be relied on by the Examiner to reject the claimed invention. The effective date of the reference is its earliest effective U.S. filing date.
When a U.S. patent application filed on or after November 29, 2000, or an application which has been voluntarily published by the USPTO is being examined, issued U.S. patents and Statutory Invention Registrations can destroy novelty under this rule, but the filing date of the associated U.S. application cannot be the filing date of a "parent" international (PCT) application.
Because the applicant's(s') filing date is initially presumed to be the date of invention, a rejection under 35 U.S.C. 102(e) may be overcome by proving a date of invention earlier than the filing date of the reference. However, the date of invention can only be carried back one year before the earliest U.S. filing date. A rejection under 35 U.S.C. 102(e) may also be overcome by proving that the invention described in the reference was not invented by "another," i.e., that the invention was invented by the same inventive entity as the current applicant(s).