A summary of the projects undertaken by the IEA Environmental Systems Activity over the period 1992 - 1994 is presented. The goal of the activity has been to investigate and evaluate systems that permit biomass conversion technologies to meet environmental requirements. The projects undertaken that produced significant outcomes were: 1. Analysis and characterisation of wastewaters from the production of bio-oils and upgraded biooils from biomass. 2. Characterisation of ash and char arising from combustion, pyrolysis and gasification processes. 3. A review of volatile emissions from biomass drying. 4. A study of the control of flue gases arising from the combustion of solid biomass, bio-oils and gasification fuel gases in furnaces, gas turbines and engines. 5. The development of a new methodology for evaluating the likely environmental impacts of bioenergy systems. Progress in each of these project areas is summarised. A comprehensive report detailing the technical outcomes of the overall activity (project by project) and providing an up to date overview of the environmental issues surrounding biomass conversion has been prepared.