This article discusses possible ways to account for how solidarity comes to be constituted. Beyond accounts tying solidarity either to identity, or to the adherence to a common normative framework, recent scholarship has underscored the role played by collective action in bringing about solidarity. In this paper, I agree that collective action has been often overlooked as a fundamental element in constituting solidarity but warn against the risk of conceptualizing the source of solidarity exclusively in terms of action. Instead, I (...) propose to understand solidarity as resulting from the continuous interaction between two different dimensions of solidarity: constitutive solidarity that centres on collective action, and constituted solidarity which centres on given identities. My paper begins by distinguishing the two meanings of solidarity – constituted and constitutive. The first referring to an (instituted) set of mutual obligations applying to a given group, the second referring to solidarity as underlying social bond, which establishes the solidarity group in the first place. The paper then goes on to discuss three different accounts of constitutive solidarity: identity-based, obligations-based and action-based. I argue that only the action-based account can conceptualise the coming about of new forms of solidarity and the changing scope of the solidarity group. Yet, such accounts are unable to conceptualise how constitutive solidarity can come to ground constituted forms of solidarity, able to endure through time. On this basis, I propose to interpret constitutive and constituted solidarity as two ‘moments’ of solidarity, one symbolically grounding the other, even if not through linear causation. Rather, constitutive solidarity is constantly evolving and constantly contributes to remap the identities depicting social reality, which ground constituted forms of solidarity. (shrink)