Despite significant negative outcomes, the co-occurrence of personality disorders (PDs) and substance use disorders (SUDs) continues to be underrecognized, and the mechanisms contributing to this co-occurrence remain unclear. This review summarizes recent work on PD-SUD co-occurrence, with a focus on borderline and antisocial PDs, general substance use patterns among those with PDs, and the association of personality traits with SUDs. The prevalence of co-occurring PD-SUD is generally high, with estimates ranging depending on the type of PD and SUD, the population assessed, and the sampling methods and measures used. Current theoretical explanations for co-occurrence include shared etiology and predisposition models, with research highlighting the importance of transactional processes. Potential underlying mechanisms include personality traits and transdiagnostic characteristics. Recent research has increased focus on substances besides alcohol, dimensional models of personality pathology, and transactional explanations of co-occurrence, but more research is needed to disentangle the nuanced PD-SUD relationship.