This book introduces the reader to the necessary technical background to study C*-algebras arising from actions of groups or semigroups

The text focuses on recent examples and techniques developed in K-Theory

It contains an introduction to Baum-Connes methods as well as a concise description of the Mackey-Rieffel-Green machine for crossed products

Much of the material is available here for the first time in book form

Joachim Cuntz is a full Professor at the Westfälische Wilhelms-Universität in Münster, Germany.

Siegfried Echterhoff is a full Professor at the Westfälische Wilhelms-Universität in Münster, Germany.

Xin Li is a Senior Lecturer in Pure Mathematics at Queen Mary University of London, United Kingdom.

Guoliang Yu is Powell Chair in Mathematics and Professor at the Texas A&M University, USA.