AbstractThe European Activation System (EASY) is a complete code and data package for the calculation of activation of materials in neutron fields. It comprises the European Activation File (EAF) and the inventory code FISPACT. EAF consists of a set of sub-files covering all the data (e.g. cross sections and decay data) required for activation calculations. These sub-files are described. The features of FISPACT that enable detailed investigation of activation properties are listed and examples of various calculations described. These examples cover: inventory calculations including pathway and uncertainty assessment, treatment of sequential charged particle reactions, inclusion of trace amounts of actinides and the modelling of a pulsed irradiation history.