Volume 38 of Reviews in Mineralogy provides detailed reviews of various aspects of the mineralogy and geochemistry of uranium We have attempted to produce a volume that incorporates most important aspects of uranium in natural systems while providing some insight into important applications of uranium mineralogy and geochemistry to environmental problems The result is a blend of perspectives and themes historical Chapter 1 crystal structures Chapter 2 systematic mineralogy and paragenesis Chapters 3 and 7 the genesis of uranium ore deposits Chapters 4 and 6 the geochemical behavior of uranium and other actinides in natural fluids Chapter 5 environmental aspects of uranium such as microbial effects groundwater contamination and disposal of nuclear waste Chapters 8 9 and 10 and various analytical techniques applied to uranium bearing phases Chapters 11 14 This volume was written in preparation for a short course by the same title sponsored by the Mineralogical Society of America October 22 and 23 1999 in Golden Colorado prior to MSA s joint annual meeting with the Geological Society of America