This paper proposes an explanation based on the concept of relative deprivation, but also reviews the criminological literature in a search for other theoretically relevant variables. After assessing problems of sampling and measurement, and using a considerably larger sample than used in previous studies, multiple regression analyses reveal positive net effects of both inequality and population growth (reflecting a higher proportion of young people) on homicide rates. Further analyses show that the effects of inequality on homicide are more pronounced in more democratic nations, a finding supporting the relative deprivation explanation. Income inequality also has stronger effects in more densely populated countries, in wealthier nations, and in countries with larger internal security forces. (Publisher abstract)