This manual describes the main directions, forms and methods of work of counterintelligence units of commercial firms and private industrial enterprises. The author paid the main attention to the problems of protecting non-state economic entities from industrial espionage, subversive activities of unscrupulous competitors, encroachments of criminal communities. The book is addressed to employees of private detective agencies, security services of commercial firms, students studying the special course "Fundamentals of Business Security," as well as those readers who are interested in intelligence and counterintelligence issues.