Galaxies, along with their underlying dark matter halos, constitute the building blocks of the universe. Of all the fundamental forces, gravity is the dominant one that drives the evolution of structures from small density seeds to the galaxies we see today. The interactions among myriads of stars, or dark matter particles, in a gravity-based structure produce a system with fascinating implications for thermodynamics, including both similarities and fundamental differences. Ignacio Ferreras presents a concise introduction to extragalactic astrophysics, with an emphasis on stellar dynamics and the growth of density fluctuations in an expanding universe. Additional chapters are devoted to smaller systems (stellar clusters) and larger ones (galaxy clusters). Written for advanced undergraduates and beginning postgraduate students, Fundamentals of Galaxy Dynamics provides a useful tool to embark on a research career. Some of the derivations for the most important results are presented in detail to enable students to appreciate the beauty of math as a tool to understand the workings of galaxies. Each chapter includes a set of problems to help students advance with the material.