This book is an introduction to statistical physics aimed at undergraduate students in physics and engineering. It may also serve as a reference for graduate students and researchers. The fact that thermodynamics and statistical physics have a very wide domain of relevance and validity, as well as a very long tradition, often leads to abstract and axiomatic presentations even for beginners. We have chosen the opposite direction, namely to discuss the key ideas and methods through concrete representative systems, and to treat general ideas as casual by-products. This choice is expressed already in the structure of the book, consisting of five parts: (I) The Kinetic Theory of Gases; (II) Statistical Physics with Paramagnets; (III) Statistical Physics and Thermodynamics, which deals with the Einstein solid and monoatomic ideal gases; (IV) From Ideal Gas to Photon Gas, which covers also equilibrium of chemical reactions and the Debye model; (V) Of Fermions and Bosons.