The Tamarin prover is an open-source analysis tool for cryptographic protocols. Given a specification of a protocol, possible adversaries, and the desired security properties, Tamarin either verifies the protocol or provides counter examples witnessing attacks. Tamarin is a robust and powerful analysis tool: it has been under development for over a decade and has reached a state of maturity where it can be applied to model and analyze a wide range of real-world cryptographic protocols. It is now one of the leading tools in this domain, with a wide and active user community spanning both academia and industry. The objective of this book is to help both researchers and practitioners to gain a general understanding of how Formal Methods tools like Tamarin can be used to analyze and improve the quality of real-world protocols. Moreover, we specifically showcase the Tamarin prover and provide guidance on its usage. In this sense, this book provides a user’s manual forTamarin. But it goes far beyond that, highlighting Tamarin’s underlying theory and its use in modeling and applications.