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Level of Personality Functioning in Adolescence: Psychological and Biological Aspects in the Context of Diagnosis and Therapy Adolescence is a crucial developmental phase in which identity, interpersonal relationships, and emotional regulation are further shaped and consolidated. These processes build upon early attachment experiences. At the same time, there is an increased vulnerability to personality disorders (PD), which are influenced by genetic and environmental factors such as abuse, neglect, and insecure attachment patterns. These factors can trigger neurobiological changes, including dysregulation of the stress and attachment system, contributing to the development of PD. This paper considers the level of personality functioning (LPF) as a central concept in the diagnosis and treatment of personality disorders. While traditional diagnostic systems (DSM-IV, ICD-10) have been criticized for their rigid categorization, recent approaches show a growing shift towards dimensional models. In DSM-5, categorical diagnosis for PD remains, complemented by the alternative dimensional model (AMPD) in the appendix. The ICD-11 has introduced a dimensional model for PD diagnosis for the first time. This allows for a more differentiated assessment of core psychological functions (identity, self-regulation, empathy, intimacy), leading to more precise diagnostics. A particular focus is placed on psychodynamic therapeutic approaches such as Transference-Focused Psychotherapy (TFP) and Mentalization-Based Therapy (MBT), which have proven to be particularly effective for young individuals with traumatic experiences. Studies indicate that these approaches positively influence psychological and neurobiological mechanisms. Future research on dimensional models, appropriate diagnostic tools, and therapeutic interventions is essential to identify impairments in LPF early, reduce stigma, and further develop personalized treatment strategies.