This advanced monograph of semigroup theory explores semigroups of linear operators and linear Cauchy problems. Suitable for graduate students in mathematics as well as professionals in science and engineering, the treatment begins with an introductory survey of the theory and applications of semigroups of operators. Two main sections follow, one dedicated to semigroups of linear operators, and the other to linear Cauchy problems. Author Jerome A. Goldstein emphasizes motivation and heuristics as well as applications. Each of the two sections concludes with further applications and historical notes. Challenging exercises appear throughout the text, which includes a substantial bibliography. This edition has been updated with supplementary transcripts of five lectures given by the author during a 1989 workshop at Blaubeuren, Germany.