The concept of entropy arises in diverse branches of science, including physics, where it plays a crucial role. However, the nature of entropy as a unifying concept is not widely discussed-it is dealt with in a piecemeal manner within different contexts. The interpretation of the concept is also subtly different in each case. This book draws these diverse threads together and present entropy as one of the crucial physical concepts. It covers a range of different applications of entropy, from the classical theory of thermodynamics, the statistical approach, entropy in quantum theory, information theory and finally, its manifestation in black hole physics. Each is presented in a manner suitable for undergraduates and interested laypersons with no previous knowledge. The book takes an overview of these areas and assesses to what extent the concept of entropy is being treated in the same way in each, and how it differs.Key Features: Provides an accessible introduction to the exciting topic of entropy. Includes the latest research on black holes, quantum theory, and the Big Bang. Contains worked examples and exercises.