This book presents a self-contained introduction to the physics of computing, by addressing the fundamental underlying principles that involve the act of computing, regardless of the actual machine that is used to compute. Questions like "what is the minimum energy required to perform a computation?", "what is the ultimate computational speed that a computer can achieve?" or "how long can a memory last", are addressed here, starting from basic physics principles. The book is intended for physicists, engineers, and computer scientists, and it is designed for self-study by researchers who want to enter the field or as the main text for a one semester course at advanced undergraduate or graduate level. The theoretical concepts presented in this book are systematically developed from the very beginning, which only requires basic knowledge in physics and mathematics.