This chapter presents an overview of bioreactor configurations for the production of biogas with an investigation of different enhancement strategies for the conversion of organic biomass to methane. Initially anaerobic digestion (AD) microbial processes are introduced. Subsequently, optimal bioreactor design is examined. The AD process is capable of converting a large variety of feedstocks to carbon dioxide and methane. The performance of microbial conversion is closely linked to feedstock characteristics. As such bioreactor concepts are explored with reference to these feedstock characteristics, and are categorized as either: liquid and low solid content AD; or high-solid AD. Enhancement strategies include the enrichment of active biomass within the reactor through immobilization of microbes, separation of process stages, solid-liquid phase separation, improvement of mass transfer, and conversion of hydrogen and carbon dioxide to methane. Recent reactor developments are considered in each section.