*This book is in the Cambria Rapid Communications in Conflict and Security Series (General Editor: Thomas G. Mahnken; Founding Editor: Geoffrey R.H. Burn) Winning Without Fighting: Irregular Warfare and Strategic Competition in the 21st Century provides an in-depth analysis of the evolving landscape of irregular warfare and its implications in an era of global crises and competition, as described in the 2022 National Security Strategy. This study defines irregular warfare as actions taken below the threshold of armed conflict-activities that do not necessitate force or violence. It highlights the role of resilience as a foundation for national defense, alongside military, political, economic, and informational measures. The book also explores ways to enhance power, legitimacy, and influence while undermining those of adversaries. By examining the historical context and theoretical underpinnings of irregular warfare and drawing on examples from China and Russia, this book demonstrates how such strategies are employed in practice and illuminates shortcomings of the American strategic culture. The implications of irregular warfare for US national security are assessed, indicating a need for a more nuanced and comprehensive approach to counter the multifaceted threats posed by adversaries adept in irregular warfare tactics. Through the lenses of competition and crises, this book advocates a holistic strategy that leverages all elements of national power and provides insights and frameworks-with a strategic reorientation to ensure enduring power, influence, and legitimacy in a rapidly evolving geopolitical landscape-to better navigate the challenges of irregular warfare.