The Greens challenge the Australian two-party system by promoting an alternative political agenda and by facilitating democratic processes. Their recent successes in federal and state elections suggest that the party itself deserves closer scrutiny. This paper shows how the Greens are organisationally different from other parties currently active in Australian politics due to both their internal processes and their parliamentary practices. Recent theories of parties argue that party organisation has changed significantly for major parties, adopting an electoral-professional or cartel model that centralises power and decision-making in party representatives within parliaments. This paper shows how a smaller party uses identity formation processes to establish a distinctive organisational style. We examine the Greens' party organisation by analysing the interdependent relationships between the party membership, the state and national offices, and Green MPs. The paper is based on original research including in-depth interviews undertaken with state and federal Greens members of parliaments.