The concept of community unionism is built on the idea that union connection to the community builds successful campaigns and strengthens unions. This paper investigates how and when this might occur, focusing first on achieving a concrete definition of community, second by establishing a framework for understanding the contours of successful community unionism and finally exploring this framework through a comparison of two case studies of community unionism from Australia and Canada. The term community has entered union discourse as union density and power, particularly in the industrialised world, has diminished. While work between unions and community organisations is not new, theoretical interest in these relationships has surged in the last 15 years (Brecher and Costello 1990a; Frege, Heery et al. 2004; Reynolds 2004). Yet the scholarship on coalitions has some limitations, often focusing on best practice case studies and assuming rather than proving if and how coalitions are a source of power for unions (Tattersall 2005).