Recently, the problem of inappropriate behavior of pets has become unusually worse. The author of this work provides very extensive material on the problem of deviant behavior, gives a comparative analysis of its causes and symptoms in children and animals, presents the results of his own theoretical and empirical research, including a description and classification of behavioral disorders in dogs, offers examination methods to identify violations in their behavior and make a diagnosis. In order to determine the level of development of the animal, a method for quantitative assessment of the development of puppies has been developed. The presentation style is consistent and quite simple, which allows not only specialists (animal psychologists, veterinarians, trainers), but also animal owners to familiarize themselves with the work.