This article reports on a two-year study of union/community organizing in the UK, USA and Australia. It takes a particular model of organizing — that of the Industrial Areas Foundation — and analyses trade union engagement in coalition-building activity in each of the three countries. Findings show mixed approaches to working with community groups from ad hoc instrumentalism to deep coalition-building. While these variations may, in part, be explained by different industrial relations contexts, it appears that the ‘fit’ between ideology and culture of unions and their coalition partners, as well as the practices and strategies that reinforce this fit, have much greater effect on the attitude and behaviour of unions towards non-workplace-based organizing. The article contributes to debates about the conditions under which unions succeed (or not) in sustaining strong coalition-building beyond their traditional constituencies.