National security is being redefined in the 21st century. Rapid advances in technology are reminiscent of the initiation of the nuclear age. As the cyber realm and outer space develop as new domains of international competition, there are new strategies and tools for states to utilize and also defend against. Important elements of national security and some strategies are not new but would benefit from exploration with a fresh perspective. This book seeks to explore some of the changing relationships, the nature of alliances, and the UN to better understand national security in the digital and information age. The framework of international law as applied to new domains and gray-zone activity will also be explored to understand the tactics being used in the current strategic environment. Examining these significant elements of national security with a modern eye provides important insights for policymakers and the public in this new age of national security.