How do I claim priority to a prior foreign patent application in a U.S. patent application?

To claim priority to an earlier-filed foreign application, the applicant must:

1. File the U.S. application within 12 months of the foreign application’s filing date (6 months for design applications).
2. In the U.S. application, include a claim for priority that identifies the foreign application. For applications filed on/after 9/16/12, this must be in an ADS.
3. File a certified copy of the foreign application, unless it was previously filed or is available to the USPTO via a priority document exchange program.

See MPEP 213 – 216 for the detailed requirements. Some deadlines can be extended on petition if unintentionally delayed.