This report focuses on domestic drug enforcement. It outlines historic development and major changes in U.S. drug enforcement to help provide an understanding of how and why certain laws and policies were implemented and how these developments and changes shaped current drug enforcement policy. In the 19th century federal, state, and local governments were generally not involved in restricting or regulating drug distribution and use, but this changed substantially in the 20th century as domestic law enforcement became the primary means of controlling the nation's substance abuse problems.