The United States’ new Defend Forward Strategy constitutes a major change in how the nation with the world’s most powerful cyber arsenal views when and how this arsenal should be deployed. It is a large step in the direction of more aggressive action in cyberspace—albeit for defensive ends. The United States has not attempted to hide this new and more aggressive cyber posture. To the contrary, it has telegraphed the change, probably in order to enhance deterrence. But the telegraphing has taken place at a highly abstract level. Very little is known about precisely what types of operations Defend Forward entails. And while the US government has asserted that Defend Forward is consistent with domestic and international law, it has not explained how the new strategy overcomes the perceived legal constraints that previously tempered US responses to cyber intrusions and threats. This volume aims to fill these gaps, and to bring Defend Forward out of the shadows, so to speak, both factually and legally.