Abstract
Biomass is a generic word used to characterise all matter created naturally. Therefore, it contains all sorts of materials and substances extracted from living organisms. Forest and farm biomass, commercial and urban residues and waste are the sources of biomass used as a bioenergy feedstock. Biomass resources suitable as biogas feedstocks, usually referred to as anaerobic digestion feedstocks, are represented by a wide variety of renewable organic materials available, ranging from simple compounds to complex high-solid substrates. They usually have a high content of sugar, starch, proteins or fats, and their ability to be easily decomposed through anaerobic digestion is a common feature. This chapter gives an overview of biomass sources for anaerobic digestion as well as their important characteristics.