This document provides an overview of a research project that identified U.S. commuting zones and labor market areas with journey-to-work data from the 1990 Census. This research replicated a previous delineation of U.S. 1980 commuting zones and labor market areas. County to county flows of commuters were analyzed with a hierarchical cluster algorithm. The results of the cluster analysis were used to identify commuting zones (i.e., group's of counties with strong commuting ties). For 1990, 741 commuting zones were delineated for all U.S. counties and county equivalents. These commuting zones are intended for use as spatial measures of local labor markets when researchers are not concerned with minimum population thresholds. Where necessary, the commuting zones were then aggregated into 394 labor market areas that met the Bureau of the Census' criterion— of a 100,000 population minimum. This was done to acquire a special 1990 Census Public Use Microdata Sample (PUMS-L) that identifies labor market areas in which individuals live and work. The commuting zones and labor market areas were also classified according to the population of the largest place within them.