The relationship between age and crime is one of the oldest known in the criminological literature. This entry describes research on what is known as the “age–crime curve,” first by reviewing recent data, then discussing historical and theoretical work. The entry then discusses policy implications of the age and crime research. These implications differ according to whether one views the relationship between age and crime as a biological “invariant” phenomenon, or as one that can be explained at least partially by social factors. Both social and biological factors likely influence the age–crime curve, and policy should be developed accordingly.