On Cyber is a groundbreaking work that fuses information security and military science to lay the foundation of an operational art for cyberspace operations. Hundreds of books have been written on the tactics of cybersecurity and dozens have been written that discuss the strategic implications of cyber conflict. But missing is a book that links the two. On Cyber fills that gap. After millennia of conflict, traditional kinetic war fighting is highly refined and captured in mature and vetted military doctrine. Cyber operations, however is constantly evolving and affords tremendous benefits alongside significant challenges. Nations around the world have raced to build cyber organizations and capabilities, but are struggling to employ cyber operations to their benefit. Some have stumbled, while others have had dramatic impact on the battlefield and global geopolitics. At the same time, companies and even individuals are now facing nation state and nation state enabled threat actors in cyberspace while their governments remain apparently powerless to protect them. Whether you are a network defender or cyber operator, On Cyber is a seminal book and the lessons you learn will help you do your job better. Importantly, network defenders will understand how nation-state threat actors think, organize, operate, and target your organization. Cyber operators will gain a glimpse into the future of cyber doctrine. The authors are perhaps the best two people to author such an ambitious work, having served on the faculty of West Point for a combined 20 years, participated in military cyber operations and training, helped architect the U.S. Army's Cyber Branch, and together possess more than 50 years of military experience.