The overcoming of professional boundaries to collaboration in patient care has become one of the goals of mental health service policy in England over the past 25 years, predominantly through the creation of community mental health teams. However, research has shown that these boundaries have been slow to come down, and some commentators have pointed to the benefits of appropriate boundaries. This paper introduces a theoretical framework, which seeks to categorise boundary activity in organisations and then examines the boundary activity of professional groups and community teams during the integration of mental health and social care service provision in one locality in the southwest of England. The paper identifies the ways in which this integration impacted on boundary activity and draws out the messages for mental health policy and practice that emerge.