This handbook was elaborated through the joint efforts of a group of biogas experts from Denmark, Germany, Austria and Greece, as part of the BiG>East project, (EIE/07/214/SI2.467620), running during the period 09.2007-02.2010, with the overall aim of promoting the development of biogas from anaerobic digestion in Eastern Europe. The project was co-funded by the European Commission, in the framework of the “Intelligent Energy for Europe” Programme. The English version of the handbook was subsequently translated into Bulgarian, Croatian, Greek, Latvian, Romanian and Slovenian, which are the languages of the countries targeted by the BiG>East project. These translated versions contain also a supplementary chapter of country specific information. The editor thanks all the authors, the reviewers and the two talented students for their contribution to the handbook and for the great team work.