The increasing demand for biomass for the production of bioenergy is generating land-use conflicts. These conflicts might be solved through spatial segregation of food/feed and energy producing areas by continuing producing food on established and productive agricultural land while growing dedicated energy crops on so called “surplus” land. Ambiguity in the definition and characterization of surplus land as well as uncertainty in assessments of land availability and of future bioenergy potentials is causing confusion about the prospects and the environmental and socio-economic implications of bioenergy development in those areas. The high level of uncertainty is due to environmental, economic and social constraints not yet taken into account and to the potentials offered by those novel crops and their production methods not being fully exploited. This paper provides a scientific background in support of a reassessment of land available for bioenergy production by clarifying the terminology, identifying constraints and options for an efficient bioenergy-use of surplus land and providing policy recommendations for resolving conflicting land-use demands. A serious approach to factoring in the constraints, combined with creativity in utilizing the options provided, in our opinion, would lead to a more sustainable and efficient development of the bioenergy sector. Unless the sustainability challenge is mastered, the interdependent policy objectives of mitigating climate change, obtaining independence from fossil fuels, feeding and fuelling a growing human world population and maintaining biodiversity and ecosystem services will not be met. Despite the advanced developments of bioenergy, we still see regional solutions for designing and establishing sustainable bioenergy production systems with optimized production resulting in social, economic and ecological benefits. Where bioenergy production has been identified as the most suitable option to overcome the given problems of energy security and climate change mitigation, we need to determine which bioenergy cultivation systems are most suitable for the respective types of surplus land, by taking into account issues such as yields, inputs and costs, as well as potential environmental and socio-economic impacts.