The basic sectors are central to the growth and vitality of any economic system, and current and accurate information regarding changes in an area's economic base is vital to local economic development planning efforts. This report provides estimates of the economic base by economic sector for North Dakota counties for the period 1960-1991. The data indicate that agriculture remains North Dakota's most important basic sector, accounting for 50 percent or more of the economic base in 31 of the state's 53 counties in 1991. The energy sectors play a significant role in the economic base of a number of western North Dakota counties. Energy extraction and conversion accounted for 50 percent or more of the economic base in seven counties in 1991. Manufacturing has been a growing segment of the state's economy in recent years. In 1991, manufacturing accounted for 15 percent or more of the economic base in seven counties. Federal activities have been a major source of growth among the state's basic sector activities in recent years, and transfer payments account for most of the growth in this economic base component over the past decade. In 1991, federal activities accounted for 50 percent or more of the economic base of five counties. Tourism also has been a growing segment of the state's economy, but it has not yet assumed a dominant role in any county.