Earth-science and mineral-resource agencies from several countries started the International Strategic Minerals Inventory in order to cooperatively gather information about major sources of strategic mineral raw materials. This circular summarizes inventory information about major deposits of niobium and tantalum, two of the mineral commodities selected for the inventory.The report was prepared by Richard N. Crockett of the British Geological Survey (BGS) of the Natural Environment Research Council and David M. Sutphin of the U.S. Geological Survey (USGS). David G. Bate, BGS, provided bibliographi~ assistance, and the report was transcribed by Dorothy J. Manley, USGS. The niobium and tantalum inventory information was compiled by Richard N. Crockett, BGS, with assistance from Richard J. Pantel, U.S. Bureau of Mines (USBM). Inventory records were additionally supplied by David A.