Self-aggressive behaviors, including non-suicidal self-injury (NSSI), constitute a growing clinical concern among adolescents and young adults. The increasing prevalence of these behaviors in this age group highlights the need for in-depth diagnostic and therapeutic reflection. The aim of this review article is to systematize current knowledge on the phenomenon of self-injury within the framework of contemporary classifications of mental disorders, such as the DSM-5 and the ICD-11, which in recent years have begun to distinguish NSSI as a separate diagnostic entity requiring further empirical investigation and refinement of diagnostic criteria. The article presents the clinical characteristics of self-injurious behaviors, including the diversity of their forms, course, frequency, and associated psychopathological symptoms, such as anxiety, depressive disorders, and personality disorders. The functions of self-injury are discussed, and epidemiological data concerning the prevalence of NSSI in adolescent populations are reviewed. Furthermore, risk factors are identified, including traumatic experiences, attachment disorders, impulsivity, impaired emotion regulation, and the presence of comorbid mental disorders. The second part of the review focuses on theoretical models explaining the etiology of self-aggressive behaviors, with particular emphasis on psychoanalytic perspectives, which conceptualize NSSI as an expression of intrapsychic conflict and unconscious aggression directed toward the self.