A strategic approach to local sustainability assessment requires that sustainability implications of proposed policies, plans and programmes are evaluated. These evaluations need to critically consider organizational structures, processes and outcomes. The establishment of 'communities of practice', groups or networks of practitioners with shared interests, is a helpful mechanism for facilitating change in a wide range of organizations. This paper analyses the potential for communities of practice to contribute to the implementation of sustainability assessments by local government. Focusing on Sutherland Shire Council in Sydney, Australia, this paper presents the findings of a project that engaged practitioners in the design of a sustainability assessment system. The establishment of communities of practice helped to break down the 'silos' created by institutional divides within local government, but this approach also raises challenges in maintaining momentum and overcoming political agendas.