The authors of the proposed book carried out a comprehensive study of the organization, structure, legal framework, personnel potential and the main areas of operational activity of the red and white special services: intelligence, counterintelligence, political investigation, information and analytical work, as well as related issues of formation and the use of intelligence apparatus, external intelligence, correspondence inspection, etc. The book is intended both for researchers, teachers, and for a wide range of people interested in the history of the Civil War, domestic intelligence and counterintelligence.