The book contains an analytical review of more than 800 studies of assertive behavior and the results of the author's own research. The qualities of assertive personalities, the influence of age, gender, family, situational, ethnic and cultural factors on assertiveness are considered. The advantages of assertiveness, the perception of assertive behavior and the expectation of its consequences, the features of assertiveness in childhood and the influence of parents and school on the development of assertiveness in children, the connection of the emotional intelligence of the child with its assertiveness were revealed. It is shown that assertiveness is positively related to psychological health and negatively related to depression and life-threatening addictions. Assertiveness in service relationships and its role in teamwork and leadership have been studied. Assertiveness training techniques are described. A reliable and valid assertiveness test is offered. Presented effective techniques of assertive behavior: techniques of hidden control and persuasion in business, family and interpersonal relationships, the ability to dispose of oneself, to make irresistible compliments and criticism without hurting, to prevent and resolve conflicts, to protect oneself from manipulation.