Technical Abstract: USDA has had an active citrus rootstock breeding program for more than 50 years. Swingle citrumelo rootstock was released from the USDA program in 1977 and has become one of the most important rootstocks for citrus worldwide. Three new rootstocks released from the USDA program between 2001 and 2007 also have outstanding potential for commercial use. All three rootstocks are easily propagated by seed, exhibit resistance or tolerance to citrus tristeza virus, and yield healthy and productive trees when grafted with a range of different scion cultivars. US-812 rootstock, a hybrid of Sunki mandarin (Citrus reticulata) with trifoliate orange (Poncirus trifoliata), was released by USDA in 2001, and exhibits good resistance to citrus blight. US-812 yields a moderate-sized tree when grafted with standard scions and induces good yields per hectare of high quality fruit when planted at standard to moderately high tree densities. US-802 rootstock, a hybrid of pummelo (Citrus grandis) with trifoliate orange, also exhibits good resistance to citrus blight, but combines this with tolerance to the Phytophthora-Diaprepes complex that is essential for some production regions of Florida. US-802 rootstock grafted with standard scions yields a large-sized vigorous tree that is highly productive of fruit. US-897 rootstock, a hybrid of Cleopatra mandarin (Citrus reticulata) with trifoliate orange, also has tolerance to the Phytophthora-Diaprepes complex, but in contrast, yields a healthy but dwarf tree when grafted with standard scions. Because of the very small tree size, US-897 should be planted at high densities for optimum fruit productivity per area. Proper matching of rootstock with tree spacing, soil, and disease conditions is essential for good performance of any citrus planting.