This PhD research aims at the development of an operational sustainability assessment tool for policy makers and stakeholders involved in bio-energy production and consumption. It intends to gain insight into the ecological and socio-economical sustainability of the most relevant combinations of local or imported biomass and conversion technologies in Flanders. Therefore, it is necessary to make an inventory and evaluation of the most relevant options of energetic valorisation of biomass in Flanders in the short and long term. The major part of the research will aim at the elaboration of an adapted and integrated sustainability model for Flanders. First, an extensive literature review of existing sustainability criteria and assessment tools, principally Life Cycle Analysis (LCA), will be performed and internationally available LCA data will be evaluated. Furthermore, economical optimisation models for the use of biomass will be evaluated. Finally, environmental, economical and social sustainability assessment aspects will be brought together into an integrated sustainability model. This model will make it possible to weigh possible biomass-conversion routes against each other with respect to sustainability, energetic efficiency and cost efficiency.