What do atomic nuclei, neutron stars, a domestic power supply, and the stunning colors of stained glass in cathedrals all have in common? The answer lies in the unifying concept of quantum fluids, which allows us to understand the behavior and properties of these different systems in simple terms. This book reveals how quantum mechanics, usually considered as restricted to the invisible microscopic world, in fact plays a crucial role at all scales of the universe. The purpose of the book is to introduce the reader to the fascinating and multifaceted world of quantum fluids, which covers different systems at different scales in the physical world. The first part of the book discusses the notion of phases solid, liquid, gas, presents basic aspects of the structure of matter and quantum mechanics, and includes some elements of statistical mechanics. The second part provides a description of the major quantum liquids, starting with the paramount case of electron fluids and their many applications in everyday life, followed by liquid helium and atomic nuclei. The authors go on to explore matter at very high densities, covering nuclear matter and compact stars, and the behavior of matter at extremely low temperatures, with the fascinating `superphases' of superconductivity and superfluidity. The topic of quantum fluids has multidisciplinary applications and this book will appeal to students and researchers in physics, chemistry, astrophysics, engineering and materials science.