William Joseph Bratton CBE (born October 6, 1947) is an American businessman and former law enforcement officer who served two terms as the New York City Police Commissioner (1994–1996 and 2014–2016). He previously served as the Commissioner of the Boston Police Department (BPD) (1993–1994) and Chief of the Los Angeles Police Department (LAPD) (2002–2009). He is the only person to have led the police departments of the United States' two largest cities – New York and Los Angeles.

Bratton began his police career at the Boston Police Department before becoming Police Commissioner in New York City, where his quality-of-life policy has been credited with reducing petty and violent crime. He was recruited to lead the Los Angeles Police Department in 2002. It was a period when the LAPD was struggling to rebuild trust after the 1991 videotaped beating of Rodney King, the 1992 Los Angeles riots, the pervasive corruption which was exposed in the late 1990s Rampart scandal, and the perjury committed by former LAPD detective Mark Fuhrman in 1995 during the murder trial of O.J. Simpson which helped produce an acquittal in that case. He presided over an era of reform and crime reduction.[4] In January 2014, Bratton returned to the post of Police Commissioner in New York City,[5] and served until September 2016.[6]

Bratton has served as an advisor on policing in several roles, including advising the British government[7] and is currently the chairman of the Homeland Security Advisory Council for the U.S. government.[8]

Bratton's policing style is influenced by the broken windows theory, a criminological theory of the norm-setting and signalling effect of urban disorder and vandalism on additional crime and anti-social behavior. He advocates having an ethnically diverse police force representative of the population,[9] being tough on gangs and maintaining a strict zero tolerance policy toward anti-social behavior.[10]