Personality development is closely linked to attachment security and mentalization or ToM. This chapter starts with listing the DSM categories for personality disorders, followed by a description of Borderline Personality Disorder or BPD in particular. In relation to ADHD and ASD, a discussion about BPD is of special clinical relevance as all three conditions are highly comorbid. Moreover, there is substantial symptom overlap, thus complicating the diagnostic picture. In my clinical experience, the majority of adult women with untreated ADHD initially present with anxiety, depression, mood dysregulation, and unstable relationships. Executive dysfunction, even if present, may not be the most distressing symptom at that time. In several cases, especially with a history of trauma exposure, the presenting signs and symptoms are likely to fulfill the DSM-V diagnostic criteria for BPD. The chapter explores the link between ASD and BPD in terms of differences in ToM and empathy. This is followed by a comparison between ADHD and BPD, both from a psychodynamic as well as cognitive-behavioral perspective. This includes a discussion of the pioneering works of Kernberg, Fonagy, and Linehan in the field of personality disorders. Lastly, the chapter examines the unique intersection of atypical neurodevelopment, trauma exposure, and early developmental processes, including mentalization.