Revision with unchanged content. In the last few years WLANs have become more and more popular, enabling access to the Internet and to private or company-internal networks all over the place. With the increasing amount of users sharing one and the same medium, running demanding applications with the need of exchanging larger and larger quantities of data, the necessity has grown to provide information interchange with satisfactory quality of service (QoS). The latter property requires among other things a MAC protocol enabling an efficient and fair medium access for competing network participants. In this book, different MAC schemes are investigated under the aspect of QoS, examining their efficiency and displaying their strengths and weaknesses. Those key elements which influence the QoS are tried to be analyzed and based on these results some propositions are presented which could be implemented in a new protocol to provide a satisfying QoS. The intention of this book is to help the reader get familiarized with existing MAC protocols, allow deeper understanding of the general functionality of medium access mechanisms and enable certain acquirement of sensitivity in the context of recognizing MAC scheme immanent problems. The book is aimed at computer scientists, students and interested readers who want to understand in more detail one of the main elements of QoS.