What is the format of an international publication number?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

The international publication number for PCT applications follows a specific format, as described in PCT Administrative Instructions Section 404:

• It starts with the two-letter code “WO”
• Followed by a four-digit year of publication
• A slant (/)
• A six-digit serial number

For example: “WO 2004/123456”

This number is different from the international application number and is used on the published international application and in the Gazette entry.