Criminologists have long recognized that both age and gender are very robust predictors of crime rates. Although it is beyond the scope of this chapter to develop an integrated theory of age and gender differences in crime, it is important to develop fuller explanations for lower rates of offending among females (of all ages) relative to males and among older persons (both male and female) relative to younger persons. The authors expect such explanations to focus on the data and the theoretical constructs that they have discussed in this chapter. Namely, the lower rates of crime by females and older persons can be viewed as consequences of gender and age differences in goals and the means to achieve them, in social control, in socialization, and in access to criminal opportunities (including those that dovetail with biological/physiological variables). Moreover, articulating the etiology of the higher levels of criminality among males and among the young should contribute to greater understanding of crime in general and of other behavioral differences between males and females, young and old. 1 table and 1 figures