An analysis of the potential land base for energy crops in the conterminous United States has identified 158.6 million ha that can grow short-rotation woody crops (SRWC) and herbaceous energy crops (HEC) without irrigation. Of this land, 145.3 million ha is currently used for agriculture as either cropland or pastureland, but agricultural land needs are anticipated to decline in the future. Both SRWC and HEC may be suitable crops for surplus cropland. Of the capable land base, 91.1 million ha is suitable for SRWC, and 131.1 million ha is suitable for HEC. Suitability is based on an assumption that the land must be capable of energy crop yields of at least 11.2 Mg ha-1 yr-1 with current technology. Most of this suitable land is in the North Central, South Central and Southeastern regions of the United States, although present predictions suggest that future cropland surpluses will occur largely in the Great Plains and Mountain regions of the United States. This paper defines the land suitable for energy crop production and estimates the yield potential of that land. Analyses of the relative economics of energy crop and alternative agricultural land uses will be required before the land base potentially available for energy crop production can be defined.