Work on the Tamarin tool started in 2010, with the goal of building a powerful model checker for security protocols that could handle features beyond the state-of-the-art.  Tamarin has since grown from a prototype verification system into a large, successful, open-source project, with contributors and users across many countries. The tool has proven to be robust and effective, and has reached a state of maturity where it has been applied to model and analyze a wide range of large-scale, state-of-the-art, cryptographic protocols.  Examples include TLS 1.3, 5G AKA, EMV (Chip and Pin, contactless), and Apple's iMessage PQ3. Tamarin is now one of the leading cryptographic protocol verification tools, with an active user community spanning both academia and industry.    This unique book provides a detailed account of how Tamarin can be used to solve practical problems in modeling and reasoning about cryptographic protocols.  This includes: - Background and motivation on Formal Methods for security - Basic protocol modeling - Using the tool and common workflows - Advanced modeling of primitives - Formalizing trace properties and observational equivalence properties - Automation support - Case studies It is illustrated with many figures and diagrams, allowing easy access to the concepts and use cases.   This book is written by four of Tamarin's authors, each with extensive experience in security and formal methods.  The book is practically oriented and is aimed at security researchers and engineers who work with cryptographic protocols and wish to learn how to rigorously specify and analyze them. This includes information security students learning about cryptographic protocols, industrial practitioners who design their own proprietary protocols, engineers involved in protocol standardization and related activities, as well as teams that evaluate protocol designs. The book is written with this diverse audience in mind, keeping the prerequisites to a minimum.