The behavior of liquid 3 He and 4 He provides one of the best and most direct examples in nature of the influence of quantum statistics on the bulk properties of matter. This second edition brings the reader up to date on liquid 4 He, liquid 3 He, and mixtures. The book describes the history of liquefying helium and the research stimulated by its fascinating and unique features. It also remarks on the new branch of low-temperature physics this research has engendered, a subject of importance to advanced undergraduates and graduate students in physics or physical chemistry.