To mark the 20th anniversary of the Australian union movement’s Organising Works programme, this article introduces a symposium discussing potential ways forward for unions. It overviews research regarding the challenges of union organising and renewal, both in Australia and internationally. It provides a broad historical perspective on the origins and progress of the grassroots Organising Works agenda initiated by the peak union bodies, the Australian Council of Trade Unions and Unions NSW. It explores how trade unions can best generate and sustain their spirit of mobilising and organising, while also ensuring the institutional legitimacy they require to effectively represent workers. Unions have had to manage the tension between two dynamics of trade union growth – the sense of movement involved in mobilising workers, and the institutional stability and legitimacy needed to represent workers. Unions have faced both the need to confront global capital restructuring through their own restructuring, and the need to renew and maintain a strong and democratic community base. To do so, they have built new networks and campaigning approaches, in order to organise an increasingly diverse and insecure workforce and build strong community links.