The present report provides an appreciation of the types and quantities of spent fuel for disposal and reviews the current state of knowledge of the behaviour of spent fuel under repository conditions. It further contains comments and discussions on technical and safety aspects specific to the disposal of spent fuel, discussed at a Technical Committee meeting held in Vienna in June 1988. Contents: 1. Introduction; 2. Type of spent fuel; 3. Effect of in-reactor operations on fuels; 4. Behaviour of spent fuel in the disposal environment; 5. Safety and environmental assessments of spent fuel as a final waste form; 6. Engineering evaluations and demonstrations of spent fuel disposal; 7. Summary.