What is Prosecution History or File Wrapper Estoppel?

The term “prosecution” in the context of patents refers to the patent application process, the process a patent applicant undertakes when submitting a patent application to the US Patent and Trademark Office (USPTO) for review and allowance.  During the prosecution, discourse occurs between the patent applicant and the United States Patent and Trademark Office (USPTO). 

The terms “prosecution history” and “file wrapper” refer to the entire collection of documents generated in the patent application that reflect the discourse between the patent applicant and the United States Patent and Trademark Office (USPTO).  “Estoppel” in this context means that a patent applicant is bound by the statements made to the USPTO during prosecution and cannot later deny or alter such statements.  He or she is “estopped” or barred from asserting a different meaning to statements.  

In the context of an infringement analysis, the file wrapper (or prosecution history) is reviewed to determine whether during the examination of the patent application the patent applicant made statements impacting the scope of the invention or meaning of patent claim language.  Applicants will often narrow patent claims during the prosecution to distinguish the invention over some prior art the patent examiner may have cited to argue against patentability of the invention. 

An applicant may sometimes narrow patent claims in response to a patent examiner’s request to better define the invention to meet the statutory requirements for patentability.  There has been much debate about whether file wrapper estoppel comes into play in this instance or only when applicant narrows the claims to overcome prior art.