Thermodynamics is an established discipline of physics for properties of matter in thermal equilibrium surroundings. Applying to crystals, however, the laws encounter undefined properties of crystal lattices, which therefore need to be determined for a legitimate description of crystalline states. Intended for readers with prior knowledge of condensed matter physics, this book emphasizes the roles played by order variables and dynamic lattices in crystals for thermodynamics of crystalline states.The crystalline state is generally heterogeneous, where order variables are in collective motion interacting with the lattice at excited levels, as witnessed in transition anomalies in dielectric crystals and from superconducting transitions in metals. The collective motion exhibits finite amplitude due to long-range order, breaking lattice symmetry that leads to a structural change. Such a non-linear process is discussed in the chapter of soliton theory, and related experimental evidences are also listed in this book.This book is divided into three parts for the convenience of readers. In Part I, basic concepts of phonons and order variables are reviewed. Part 2 is devoted to discussions of binary transitions, and in Part 3 we discuss superconducting transitions in simple metals.