In this chapter, students will learn how cybersecurity has become a key issue in global security. Once the primary domain of military and intelligence activities, cyber attacks and intrusions have had a broad impact, from the attacks against Georgia and Estonia to Stuxnet, to the disruption against Sony Pictures Entertainment. Cyber capabilities are no longer solely the province of states. Non-state actors, such as criminals, terrorists and ‘hacktivists’, have adapted cyber power for their own purposes. Private businesses find themselves on the frontline of cyber conflict every day. Rapidly evolving computer technology is a considerable challenge to standard strategies of conflict and deterrence as well as to the creation of norms.