The book outlines the basics of the doctrine of combustion of solid, liquid and gaseous substances. The phenomena occurring in combustible substances during heating and preceding their combustion are also disassembled. Physical and chemical properties determining the fire hazard of substances and methods for their determination are described in detail. Considerable attention is paid to the theory of combustion according to the latest data obtained on the basis of numerous studies of the phenomenon of combustion in the CCSS. The book is intended as a manual for students of fire-technical schools, courses, fire officers and persons specializing in the field of fire.