A form of claim in which the preamble acknowledges the prior art and then proceeds to describe and claim an improvement to the prior art. Jepson claims can go so far as to recite “the invention as set forth in patent __, with the addition of …” but usually they simply recite and reiterate a prior art description or claim language from an earlier patent before adding elements. Jepson claims are frequently used to secure blocking patents and force a cross license.