This book offers a new perspective on one of the defining security and intelligence challenges of the twenty-first century. Rather than treating foreign interference as a recent digital phenomenon, the book reveals it to be an enduring form of coercive statecraft that has evolved alongside changing political, institutional, and technological environments.Drawing on history, clear definitions, and systematic analysis, the book provides a disciplined framework for identifying, comparing, and assessing interference across sectors, countries, and time. It analyzes financial pressure, information manipulation, cyber intrusion, legal weaponization, and societal coercion as interacting tools rather than isolated threats.Designed for security professionals, intelligence analysts, defense planners, policy advisors, and senior public servants in national security, foreign affairs, and public safety, the book addresses the defense, security, and intelligence community. It offers practitioners analytical clarity and structured assessment tools for evaluating foreign interference as coercive power below the threshold of armed conflict.