In this volume, the authors present a self-contained introduction to discrete mathematics - the science of finite and countably infinite structures. In addition to taking a theoretical approach, they also include many practical exercises. The text covers a broad range of topics such as propositional logic, set theory as well as detailed treatments of combinatorics and graph theory. This is complemented by an extensive introduction to modern cryptography, including the RSA cryptosystem, "postquantum" systems, and the numbertheoretic and algebraic prerequisites thereof.