The conversion of research and test reactors from the use of fuel containing highly enriched uranium (HEU) to fuel that employs low-enriched uranium (LEU) has become an important issue in many Member States. The IAEA has supported several projects and activities assisting in the reduction of the use of HEU. However, no comprehensive publication addressing the rationale of qualification of these fuels had yet been available. Developed in order to meet this need, the present publication provides good practices and points of reference for the type, quality and completeness of the information to be generated in order to ensure acceptable performance of high density LEU fuels to be used in research reactors. Furthermore, it elaborates on the development and qualification of high density fuels of the type used in most research and test reactors and assesses the different approaches to the qualification process.