tatistical Mechanics and Entropy? is an edited book consisting of 16 contemporaneous open-access articles that highlight different aspects of the definition of entropy in statistical mechanics and other fields. The book includes a reflection on the real physical meaning of thermodynamic entropy, and several misconceptions regarding the violation of the second law of thermodynamics by perpetual motion machines, Maxwell?s demon, vortex tube, etc. It overviews the concept of generalized Boltzmann-Gibbs entropy in dynamical systems (e.g. Kolmogorov?Sinai entropy), information theory (e.g. R?nyi and Shannon entropies), and statistical physics (e.g. Tsallis entropy). It includes quantum modifications and extensions of equilibrium statistical mechanics. Fundamental laws of nature and thermodynamics are expanded from classical simple systems to quantum systems, as well as to more complex systems in biology, cosmology, economy and communication networks. Reading this book requires some knowledge in thermodynamics, calculus and differential equations. This book is intended to reach an academic audience ranging from undergraduate students to experienced researchers.