Borderline Personality Disorder (BPD) is a common and serious psychiatric disorder associated with severe impairments in functioning and heavy use of healthcare resources. Dialectical Behaviour Therapy (DBT) is an effective treatment for BPD, but is difficult to implement outside research environments due to its intensity and length. It is likely that DBT skills training drives the key change process for superior BPD outcomes. This project aims to explore the effectiveness of the three DBT skills modules, specifically the differential effects of the modules on skills they are purported to improve. It is being conducted across five public mental health service sites in south-east Queensland. Research into the mechanisms of action of DBT within routine clinical settings has potential important clinical, economic, and public health benefit.