This book gives an up-to-date account of the theory of one-parameter semigroups of linear evolution equations. It contains a systematic discussion of the spectral theory and the qualitative behavior of semigroups as well as many applicaions to partial differential equations, functional differential eqyations and Volterra equations. This book is written for students and researchers interested in the theory of strongly continuous semigroups and in the applications of semigroup theory.