This publication evaluates the different coolant options considered for nuclear applications with a fast neutron spectrum (i.e. fusion, fission and accelerators), compiles the latest information in the field and identifies research needs. In this study, systems cooled by light and heavy liquid metals, molten salts, as well as gas and water choices are analysed and discussed. This TECDOC documents the present state of knowledge in the area of fusion, fission and accelerator applications, and the major progress in methods and approaches made in the past years based on observations, experimental findings and operational experience. Moreover, it identifies knowledge gaps and addresses near term research and development efforts required to overcome them.