Crime after World War II spiked in the United States, leaving many scholars of crime puzzled as to its causes. Using official crime statistics and data from newly developed self‐report surveys, analysts began to unravel the relationship between an individual's lifestyle and daily activities and their risk of victimization. The data revealed that as people moved outside their homes for work and became more social out in their communities, their victimization risk increased. Data from official and self‐report surveys supported a theory of crime that suggested that as people come into contact with motivated offenders, their risk of being victimized increases. Theorists aptly named this approach “routine activity theory.” Over the next several decades, routine activity theory has become one of the most popular theories of crime, due, in part, to the evidence in support of its claims. Moreover, the theory has straightforward implications for law enforcement and crime prevention. This entry reviews the history behind routine activity theory, early research on the theory, the current empirical status of the theory, the policy implications of the theory, and its future.