The invention protected by a patent is defined in the claims.  Those claims must be new -- they must not cover anything previously published.  The applicant can amend the claims during prosecution of a patent application to grant, particularly to avoid newly-discovered earlier publications, covered by the claims.  In doing so, the applicant can change the claims so that they no longer cover subject matter that the original application taught as part of the invention.

One way to amend claims is to add a disclaimer.  A disclaimer is a negative limitation.  For example, if a claim relates to treating a broad class of disease, a disclaimer would exclude a specific disease within that broad class.

Applicants do not often use disclaimers because the European Patent Office (EPO) has strict rules that an applicant cannot add subject-matter to the application after it is filed.  Unless the disclaimer is, unusually, in the application on filing, the circumstances which allow an applicant to introduce a disclaimer are rare.

The current conditions, under which "undisclosed" disclaimers are allowable, were set out by the Enlarged Board of Appeal (EBA), the highest appeal body at the EPO, in the decision (G1/03)...

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