Analytic studies of criminal behavior have tended to concentrate on motivation or opportunity; this study examines the effect of both on crime. Economic specialization data were used to index potential opportunity structure; socioeconomic status data were used to index potential motivational structures. At the aggregate level, murder and assault were associated with motivational variables. Burglary and larceny, motor vehicle theft, and robbery were associated with opportunity variables. Rape was associated with both opportunity and motivational variables. In general, except for the highly affective crimes of murder and assault, including information about aggregate opportunity structures adds to the analysis if intermetropolitan crime patterns and makes it possible to see a plausible reason why some types of cities have high or low crime rates. Tabular data and 39 notes are provided. For related papers, see NCJ 74011. (Author abstract modified)