<Tr> <Th_colspan="2"> Chronology </Th> </Tr> <Tr> <Th> Related shows </Th> <Td> Law & Order franchise </Td> </Tr> <P> Law & Order is an American police procedural and legal drama television series, created by Dick Wolf and part of the Law & Order franchise . It originally aired on NBC and, in syndication, on various cable networks . Law & Order premiered on September 13, 1990, and completed its 20th and final season on May 24, 2010 . At the time of its cancellation, Law & Order was the longest - running crime drama on American primetime television . Its record of 20 seasons is a tie with Gunsmoke (1955--75) for the longest - running live - action scripted American prime - time series with ongoing characters . Although it has fewer episodes than Gunsmoke, Law & Order ranks as the longest - running hour - long primetime TV series . Gunsmoke, for its first six seasons, was originally a half - hour program . </P> <P> Set and filmed in New York City, the series follows a two - part approach: the first half - hour is the investigation of a crime (usually murder) and apprehension of a suspect by New York City Police Department detectives; the second half is the prosecution of the defendant by the Manhattan District Attorney's Office . Plots are often based on real cases that recently made headlines, although the motivation for the crime and the perpetrator may be different . </P>

How long was law and order on the air