Esteemed professor of physics, Don S. Lemons, offers an accessible guide to entropy. Striving to explore the subject in as simple a manner as possible, this book helps readers understand the elusive concept of entropy. Derivations are worked through step-by-step and important applications are highlighted in over 20 worked examples. Innovative aspects of the book include the construction of statistical entropy, the derivation of the entropy of classical systems from purely classical assumptions, and a statistical thermodynamics approach to the ideal Fermi and ideal Bose gases.