The reprocessing of nuclear spent fuel generates highly radioactive liquid wastes (HLW) that must be isolated from the biosphere in very durable solid matrices. In the first part of this book, generalities are presented on the radionuclides occurring in HLW and on the main characteristics and preparation methods of waste forms (glasses, ceramics, glass-ceramics) for the immobilisation of separated or non-separated wastes. In the second part, the characteristics of two categories of long-lived radionuclides (135Cs and minor actinides Np, Am, Cm) and the main matrices proposed for their specific immobilisation are reviewed. Results are presented on ceramic and glass-ceramic matrices developed for the conditioning of Cs (hollandite) and minor actinides (zirconolite, zirconolite-based glass-ceramic) and studied in the authors' laboratory.