An infringement opinion is a detailed legal study of a patent in relation to a piece of technology to determine whether the technology infringes any one valid claim of the patent. Often such an opinion becomes necessary when, for instance, you are accused of infringing the patent of another. The opinion seeks to determine whether the accusation has merit, and thus guides you in deciding how to resolve the matter. For instance, does it make sense to cease the infringing activity, purchase a license, or fight?