What is considered ‘proof of unavailability’ for a non-signing inventor?

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.

Proof of unavailability for a non-signing inventor can include various forms of evidence. According to MPEP 409.03(d):

In the case of unavailability, proof of the inability to find or reach the non-signing inventor after diligent effort must be submitted.

This proof may include:

• Returned correspondence
• Copies of email or other communication attempts
• Statements from people with knowledge of the inventor’s unavailability
• Documentation of searches or inquiries made to locate the inventor

The key is to demonstrate a diligent effort to locate and communicate with the non-signing inventor.