While the long-term storage of high-level wastes is just starting in some countries, low and medium-level wastes have been stored for several decades. Further, interim storage of spent fuel has been extended at many locations far beyond the intended time span. One of the priorities of this book is a discussion of the deleterious effects observed under these storage conditions, or under simulated storage condition tests. One chronic problem is the possibility that microbially-influenced corrosion could be occurring in the wet storage of spent fuel, thereby initiating or accelerating corrosion. Another problem is the presence of biofilms which may be breaking down the structure of waste forms, thereby jeopardizing their integrity. The book is organized around four topics: policy matters, fundamental technical issues, microbial processes in the interim storage of spent nuclear fuel, and repository storage of spent fuel. Some of the data presented indicates that previous engineering conditions are changing or deteriorating at a different rate (faster or slower) than predicted. Fundamental issues include microbial biofilm development on matrices, microbial influenced corrosion, and bioaccumulation of radionuclides.