From the year 2021 on, heavy metals from Swiss municipal solid waste incineration (MSWI) fly ash (FA) must be recovered before landfilling. This is predominantly performed by acid leaching. As a basis for the development of defined recovery rates and for the implementation of the recovery process, the authorities and plant operators need information on the geochemical properties of FA. This study provides extended chemical and mineralogical characterization of all FA produced in 29 MSWI plants in Switzerland. Acid neutralizing capacity (ANC) and metallic aluminum (Al0) were additionally analyzed to estimate the effort for acid leaching. Results show that all FA samples are composed of similar constituents, but their content varies due to differences in waste input and incineration conditions. Based on their geochemical properties, the ashes could be divided into four types describing the leachability: very good (6 FA), good (10 FA), moderate (5 FA), and poor leaching potential (8 FA). Due to the large differences it is suggested that the required recovery rates are adjusted to the leaching potential. The quantity of heavy metals recoverable by acid leaching was estimated to be 2420 t/y Zn, 530 t/y Pb, 66 t/y Cu and 22 t/y Cd.