The book "Entropy and Information Theory" by Robert M. Gray is a comprehensive treatise on the theory of probabilistic information measures and their applications to coding theorems for information sources and noisy channels. The second edition, published in 2011, has been revised and expanded to include new material and corrections. The book emphasizes source coding and stationary codes, aiming to develop Shannon's mathematical theory of communication for single-user systems. It covers fundamental concepts such as entropy, mutual information, conditional entropy, and relative entropy, along with their properties and asymptotic behavior. The book also explores the interplay between distortion and entropy, distortion and information, and the properties of good source codes. It includes three new chapters on these topics and integrates ergodic theory to provide a deeper understanding of the subject. The book is self-contained, with prerequisite results on probability and ergodic properties found in the first edition, and it aims to bridge the gap between mathematical theory and engineering applications.The book "Entropy and Information Theory" by Robert M. Gray is a comprehensive treatise on the theory of probabilistic information measures and their applications to coding theorems for information sources and noisy channels. The second edition, published in 2011, has been revised and expanded to include new material and corrections. The book emphasizes source coding and stationary codes, aiming to develop Shannon's mathematical theory of communication for single-user systems. It covers fundamental concepts such as entropy, mutual information, conditional entropy, and relative entropy, along with their properties and asymptotic behavior. The book also explores the interplay between distortion and entropy, distortion and information, and the properties of good source codes. It includes three new chapters on these topics and integrates ergodic theory to provide a deeper understanding of the subject. The book is self-contained, with prerequisite results on probability and ergodic properties found in the first edition, and it aims to bridge the gap between mathematical theory and engineering applications.