Background Rehabilitation of urban brownfield areas is a priority for many European countries since it helps facilitate land-use planning, integrated socio-economic developments and reduces pressure on the use of greenfield sites. However, past industrial activities in derelict urban sites have left serious problems in the form of polluted soils that inhibit development potential. Objectives This LIFE project aimed to demonstrate the technical and economic feasibility of compost bioremediation technology as a process for reclaiming polluted brownfield sites. Expected benefits included: accelerated decontamination processes; accelerated rehabilitation of brownfield sites; integration of environmental considerations into urban planning; and integration of new socio-economic activities within European cities’ sustainable development strategies. Results The project was implemented in the Basque Country, where numerous brownfield sites exist due to the industrial past of most cities. All the foreseen tasks were achieved and outcomes successfully demonstrated the technical, economic and environmental feasibility of biological processes as an innovative method for soil remediation in brownfield sites. Work carried out confirmed the effectiveness of adding enriched compost to brownfield soils as a useful technique for stimulating microbial growth. Mineral oil concentration was decreased by up to 88%, significantly improving soils toxicity by the end of the project period. Degradation rates of contaminants were also improved and optimum conditions allowed time savings of 53%, compared to conventional bioremediation methods. Soil organic contamination levels were lowered to below 400 ppm within a six month period using the new treatment method. This represents a considerable development on traditional systems that normally require two years to achieve an equivalent reduction. These direct environmental results are augmented by indirect advantages compared to standard approaches such as: avoiding pollution to ground water; limiting negative effects on human health; lowering energy demands; and eliminating contaminated land being dumped in landfills (with the subsequent benefits on water, soil, air resources). A guide was developed describing the BATs for remediation of contaminated soils, as well as a tool to select the best adapted techniques, depending on the type of contaminant present in each soil. This tool will assist local, national and EU policy-making as well as legislation preparation and decision making processes. No significant risks were identified that could condition the use of the technology. Economic feasibility and future potential have been confirmed through detailed and concrete figures highlighting low application cost and general high cost-effectiveness of the technology (application costs have been estimated at 0.023 €/kg of soil, being 94% lower than the cost of incineration and 80% lower than the land filling technique). A range of quality dissemination products were delivered to promote the project among EU stakeholders. These featured a project video and technical seminars which highlighted the project’s relevance and demonstration value. In addition to the project’s strong transferability benefits other tangible legacies from the LIFE project include the new physical developments (museum and housing scheme) that are being built on the reconditioned test sites.