The back-end of the nuclear fuel cycle has become the Achilles Heel of nuclear power. After more than 50 years of effort, there are, at present, no operating nuclear waste repositories for the spent nuclear fuel from commercial nuclear power plants or for the high-level waste from the reprocessing of spent fuel. The articles in this issue of Elements describe the status of geological disposal in salt, crystalline rock, clay, and tuff, as presently developed in five countries.