This article reports on a study of trade union involvement in the Sydney Alliance – a broad-based community coalition organising for the ‘common good’. The article explores three main issues: the factors motivating unions to get involved in community-based organising; whether unions have the resources and capabilities to maintain long-term involvement with organisations outside the labour movement; and whether or not engagement creates the potential for rethinking union organising. Findings suggest that taking part in the Sydney Alliance has created opportunities for unions to reflect and act upon internal organisational change to facilitate revitalisation and member participation; to improve the public image of unions and their engagement with civil society networks; and to counteract the loss of political influence with the Labor Party. At the same time, union contribution to the coalition has also proved difficult to sustain, in the main because of the lack of strategic capability of unions.