In the first phase of the procedure for the siting of hazardous waste landfills, we have to define the siting criteria for all the facilities of the solid waste management system. In order to have an idea, the following facilities were considered in our case study: hazardous waste landfills; non-hazardous waste landfills; inert waste landfills; waste-to-energy plants; MBT plants; composting and anaerobic digestion plants. The criteria sets (one for each single type of facility) can be defined on the base of existing national and regional legislation, regulations, experiences and expertise, and should cover natural, socio-economic, technical and environmental aspects.