In this chapter, we discuss the nature and aetiology of Autism Spectrum Disorder (ASD) and Personality Disorder (PD), both individually and in their comorbidity. The commonalities and differences of the diagnostic constructs will be discussed from a clinical perspective with the use of two case examples from forensic impatient and community settings. Then, clinical and research implications, along with our reflections from working with individuals with complex emotional, behavioural, personality, and neurodivergent issues in forensic settings, will be presented. For the purposes of this chapter, we will be using the established terms of ASD and PD for ease of reference. However, it is important to note that as the scientific community’s understanding of neurodivergence expands, more of what has been defined as ‘disorders’ are recognised as variations of the human condition. The risk of such terms and labels leading to stigma and pathologising difference is increasingly acknowledged; therefore, such terms should be used with caution.