Biomass or bioenergy is attracting growing attention as a sustainable and renewable energy source, which is abundant and available around the world. There are many studies on bioenergy potentials with estimates ranging from less than 100 EJ/yr to more than 500 EJ/yr in 2050. Some studies indicate that by 2100 more than 1000 EJ/yr is conceivable. To comprehend the magnitude of the estimates, the world energy supply in 2004 was 470 EJ. Bioenergy is therefore capable of playing a considerable role in energy supply both globally and regionally. The objective of this paper is to review studies on bioenergy potentials in order to identify and discuss the reasons for the varying estimates and the factors that influence realising bioenergy potentials. First, the availability of land and the magnitude of yields for energy crops are disputed in the studies. Second, the boundaries between the types of bioenergy potentials (theoretical, geographical, technical, economic, and implementation) are blurred. Third, there are different methodologies applied in the studies. Fourth, there are dynamic factors that shape bioenergy potentials. This paper concentrates on the major dynamic factors influencing the development and diffusion of energy crops. Dynamic factors are predominantly external factors to bioenergy systems, including food demands and agricultural policy and management. Additionally, there are internal factors within bioenergy systems, including productivity improvements and sustainable management of soils, water, and ecosystems. Interacting with the dynamic factors are conflicting interests and catalysing synergies.