Biomass resources for biogas, also referred to as anaerobic digestion feedstock or biogas feedstock, include various categories of organic materials. This chapter highlights the main characteristics of biogas feedstocks including their suitability, availability, digestibility and purity. Although the feedstock for biogas can be categorized according to various criteria, this chapter groups them according to their sectors of origin (agricultural, industrial, municipal and aquatic), highlighting the merits and limitations of the most utilized feedstock types within each category. The basics of feedstock availability, supply and logistics and their influence on issues related to biogas plant location are also emphasized.