This document traces the evolution of law enforcement and the criminal justice system from ancient times to the present. It discusses early systems of law from Egypt, Greece and Rome, followed by developments in medieval England like the Frankpledge system, tithing system, and Magna Carta. It then covers watch and ward systems from the 1500s, the role of sheriffs, and the establishment of the first police forces in 17th century Boston and London. The document concludes by outlining the traditional three eras of policing: the political era from 1840-1930, the reform/professional era from 1930-1980, and the community-focused era from 1980 to present.