During the last three decades, there has been considerable research devoted to the symbolic analysis of security protocols and existing tools have had considerable success both in detecting attacks on protocols and showing their absence. Nevertheless, there is still a large discrepancy between the symbolic models that one specifies on paper and the models that can be effectively analyzed by tools. In this paper, we present the Tamarin prover for the symbolic analysis of security protocols. Tamarin takes as input a security protocol model, specifying the actions taken by the agents running the protocol in different roles (e.g., the protocol initiator, the responder, and the trusted key server), a specification of the adversary, and a specification of the protocol’s desired properties. Tamarin can then be used to automatically construct a proof that the protocol fulfills its specified properties, even when arbitrarily many instances of the protocol’s roles are interleaved in parallel, together with the actions of the adversary.