I. INTRODUCTION

The Federal Circuit’s decisions in Knorr-Bremse and Seagate significantly altered the legal landscape with respect to the need for and use of opinions of counsel in patent infringement actions. The Knorr-Bremse decision eliminated the adverse inference previously applied when an accused willful infringer failed to obtain or did not produce an exculpatory opinion of counsel. The Seagate decision raised the level of proof required to find an accused infringer liable for willful infringement and clarified when attorney-client or work product privilege would be waived by an accused infringer relying on an opinion-of-counsel defense. Opinions of counsel continue to play an important role in patent litigation in the wake of these decisions. This paper explores the legal history of the Knorr-Bremse and Seagate decisions, notes recent trends and developments in the application of these decisions, and discusses advising clients on whether and when to obtain an opinion letter and what factors to consider in producing such opinions.