What is the difference between derivation and priority of invention?

While both derivation and priority of invention relate to inventorship, they focus on different aspects. The MPEP explains this distinction clearly:

Although derivation and priority of invention both focus on inventorship, derivation addresses originality (i.e., who invented the subject matter), whereas priority focuses on which party first invented the subject matter.

In other words:

• Derivation (under pre-AIA 35 U.S.C. 102(f)) is concerned with whether the named inventor actually invented the claimed subject matter or derived it from someone else.
• Priority of invention is about determining which party was the first to invent the subject matter when there are competing claims to the same invention.

This distinction is important in pre-AIA patent law, particularly in interference proceedings and in assessing the validity of patent claims.

To learn more:

• derivation
• priority of invention
• inventorship
• pre-AIA patent law