Our last article in the March/April 1995 issue of GEOPHYSICS discussed patentability and the requirements for obtaining a patent. This article addresses the issues surrounding patent infringement. Patent infringement is a concept that is very much misunderstood by lay managers, scientists and engineers. The purpose of this article is to provide a basic understanding of patent infringement issues. Two commonly recurring misunderstandings that we address involve (1) the belief that a patent allows the holder to practice the patented invention (it does not!), and (2) the scope of a patent.