Law360, New York ( July 6, 2015, 12:08 PM EDT) -- A patent claim is functional if it defines the claimed invention in terms of what it does rather than what it is. Over the last 20 years, the U.S. Court of Appeals for the Federal Circuit relaxed restrictions on the construction of functional claims — leading to a sharp increase in their number. The Federal Circuit's recent decision in Williamson v. Citrix Online LLC calls these functional claims into question. Williamson signals a possible return to old restrictions on functional claiming and, in particular, a return to "means-plus-function" claiming: limiting a functional claim to what is disclosed by the specification, or equivalents. Such a return threatens to significantly narrow the scope, and impact the validity, of software patents that rely on functional claiming. Innovators and practitioners should therefore closely evaluate what Williamson means for their offensive and defensive patent strategy and should put a plan in place to deal with its potential implications....