Cryptology is the art and science of secure communication over insecure channels. The primary aim of this book is to provide a self-contained overview of recent cryptologic achievements and techniques in a form that can be understood by readers having no previous acquaintance with cryptology. It can thus be used as independent reading by whoever wishes to get started on the subject. An extensive bibliography of 250 references is included to help the reader deepen his or her understanding and go beyond the topics treated here. This book can also be used as preliminary material for an introductory course on cryptology. Despite its simplicity, it covers enough state-of-the-art material to be nevertheless of interest to the specialist. After a survey of the main secret and public key techniques, various applications are discussed. The last chapter describes 'quantum cryptography', a revolutionary approach to cryptography that remains secure even against an opponent with unlimited computingpower. Quantum crytography is based on the principles of quantum physics.