The book is devoted to debugging programs of medium complexity or small blocks of software systems. The methods and typical means of performing the main works that make up the debugging of programs are described, methods and techniques for developing programs that prevent the occurrence of errors and facilitate their detection and elimination are considered. The general debugging methodology set forth in the book, as a rule, does not depend on the algorithmic languages ​ ​ and specific debugging tools used, but examples are given for PL1, fortran, algol and for EC OS computers.