An opinion obtained from legal counsel to the effect that a product or process does not render the recipient liable for infringement of certain third-party intellectual property rights. In U.S. law, such an opinion can provide a good faith basis for a belief that a product is non-infringing (i.e., that there was no willful infringement) and is therefore highly relevant evidence in determining whether a prevailing plaintiff should received enhanced damages and attorneys’ fees.
Such an opinion must be “competent,” which can mean a number of things, for example precluding a simply conclusive opinion written in essence by a “hired gun,” rather requiring that the opinion be a considered application of the law to the patent, that the opinion writer be independent (i.e., outside counsel), and have considered the prosecution history (or file wrapper) of the patents and should credibly and logically explain, based on a review of relevant facts, the reason or reasons that no liability arises, e.g., invalidity, unenforceability or non-infringement.
Privilege is usually waived in such opinions in the course of a patent infringement suit, as well as related communications with the opinion writer. Formal antitrust opinions may also be sought on antitrust issues so as to provide a good faith basis to believe in the legality of agreements, understandings, and practices.