When an invention is improved after a patent application disclosing the invention has been filed, a new patent application, known as a Continuation-In-Part, and abbreviated as CIP, is filed to include the improvement. Prior art that arose after the filing date of the original patent application but not after the filing date of the CIP can be cited against the CIP.

A continuation-in-part is an application filed during the lifetime of an earlier nonprovisional application, repeating some substantial portion or all of the earlier nonprovisional application and adding matter not disclosed in the said earlier nonprovisional application. (In re Klein, 1930 C.D. 2, 393 O.G. 519 (Comm’r Pat. 1930)). The continuation-in-part application may only be filed under 37 CFR 1.53(b). The continuation-in-part application must claim the benefit of the prior nonprovisional application under 35 U.S.C. 120 or 365(c).