Deterrence theory was well developed during the Cold War for the deterrence of kinetic attacks. While the deterrence of cyber attacks is one of the most important issues facing the United States and other nations, the application of deterrence theory to the cyber realm is problematic. This study offers an introduction to cyber warfare and a review of the challenges associated with deterring cyber attacks. Mazanec and Thayer recommend efforts in three specific areas to aid the deterrence of major cyber attacks: by cultivating beneficial norms for strategic stability; by continuing efforts in the area of improving cyber forensics and defences; and, finally, by developing and communicating a clear declaratory policy and credible options for deterrence-in-kind so as to make escalation unavoidable and costly. This timely study reflects increased international interest in cyber warfare, and is based on the recognition that information networks in cyberspace are becoming operational centres of gravity in armed conflict.