The reduction to practice is a United States patent law concept. It means the embodiment of the concept of an invention. The date of this embodiment is critical to the determination of priority between inventors in an interference proceeding.

Conception is the "formation in the mind of the inventor, of a definite and permanent idea of the complete and operative invention, as it is hereafter to be applied in practice." Hybritech Inc. v. Monoclonal Antibodies, Inc., 802 F.2d 1367, 1376 (Fed. Cir. 1986) (quoting 1 Robinson On Patents 532 (1890))

The embodiment of an invention can either be:

• Actual reduction to practice: "[R]equires that the claimed invention work for its intended purpose." Brunswick Corp. v. U.S., 34 Fed. Cl. 532, 584 (1995).
• Constructive reduction to practice: "[O]ccurs upon the filing of a patent application on the claimed invention." Brunswick Corp. v. U.S., 34 Fed. Cl. 532, 584 (1995).
• Vicarious reduction to practice: A legal doctrine that presumes one party's actual reduction to practice of an invention as the opposing party's actual reduction to practice. If A proves this method works. The same method used by B must work. The doctrine is usually more important in a multiple party interference.

Some types of evidence

In addition to inventor's notebook, several additional kinds of evidence can be used to establish an earlier priority date.

Working model

A "working model" is usually a strong evidence to demonstrate actual reduction to practice. Unlike patent models of the 18th and 19th century, a working model is no longer a requirement of the U.S. patent law. However, if the inventor builds a working model for testing and for displaying to potential buyers, it can also be used to prove an earlier than filing priority date.

Disclosure Document Program

The Disclosure Document Program (DPP) is a USPTO program that allows an inventor to file a preliminary description of his/her invention. The filing of this preliminary finding can be used to establish a date of conception before applying for a patent.