The first section of this article considers the relationship between the theory and empirical data in the studies of homicide in the United States. The author examines the role that theory plays in understanding the data and therefore what may be predicted based on those data. The second section reviews some of the major concepts derived from the empirical study of homicide in the United States and that are used in the theoretical explanations in those studies. The third section presents a preliminary analysis of some of the data from a study designed to evaluate American theories of homicide using European data. By using European state data to test American theories derived from State-level data in the United States, the objective is to assess the adequacy of these theories in explaining homicide outside of the American experience. Based on the findings, the association of the murder rate and the unemployment rate apparently are contingent upon the association of the murder rate with the robbery rate. Without exception, where those two crime rates are highly correlated, the murder rate correlates with the unemployment numbers; where the two crime rates are not highly correlated, there is no significant correlation of murder with unemployment. Some implications of these findings for future research are suggested. 1 table, 25 footnotes, and 4 references