Gray zone conflict is a term that has been introduced by American strategists to describe the new reality of international conflict below the threshold of war and violence. The book aims to provide a broad overview of the covert and overt ambiguous measures hostile actors use to weaken the U.S. and the West more generally, including gray propaganda, disinformation, covert political influencing, foreign media operations, cultural influence, migration, financial destabilization, the use of protest movements, and even covert attacks using proxies and high-tech weaponry. The main argument is that these efforts of covert destabilization have historical precedents and that the Cold War provides a suitable paradigm for understanding and analyzing the current threats. The book relies on historical examples to illustrate how techniques have been used in the past and links them to practices and techniques used by U.S. adversaries today. The final chapter of the book lays out strategy options for preventing, deterring, and mitigating covert and ambiguous attacks on the U.S. by foreign powers.