This textbook offers an accessible introduction to counterinsurgency operations, a key aspect of modern warfare. Featuring essays by some of the world's leading experts on unconventional conflict, both scholars and practitioners, the book discusses how modern regular armed forces react, and should react, to irregular warfare. The volume is divided into three main sections: Doctrinal Origins: analysing the intellectual and historical roots of modern Western theory and practice Operational Aspects: examining the specific role of various military services in counterinsurgency, but also special forces, intelligence, and local security forces Challenges: looking at wider issues, such as governance, culture, ethics, civil-military cooperation, information operations, and time. Understanding Counterinsurgency is the first comprehensive textbook on counterinsurgency, and will be essential reading for all students of small wars, counterinsurgency and counterterrorism, strategic studies and security studies, both in graduate and undergraduate courses as well as in professional military schools.