Law & Order is an American police procedural and legal drama television series created by Dick Wolf and produced by Wolf Entertainment and Universal Television, launching the Law & Order franchise.

Law & Order aired its entire run on NBC, premiering on September 13, 1990, and completing its 20th season on May 24, 2010. On September 28, 2021, after an 11-year hiatus, NBC announced that the series would be revived for a 21st season, which premiered on February 24, 2022. The revival saw the debut of new regular cast members, and the reprise of two roles by series veterans: District Attorney Jack McCoy (Sam Waterston), and Detective Kevin Bernard (Anthony Anderson). Afterwards, the series was renewed for three additional seasons. In May 2025, it was announced the series had been renewed for its twenty-fifth season, which premiered on September 25, 2025.

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 homicide detectives, while the second half is the prosecution of the defendant by the Manhattan district attorney's office. Plots are based on real cases that recently made headlines, although the motivation for the crime and the perpetrator may be much different.

The show started using revolving door casting in season two. The progression of the record for longest serving main cast members of the series is: Jerry Orbach as Detective Lennie Briscoe, S. Epatha Merkerson as Lieutenant Anita Van Buren and Sam Waterston as Executive Assistant District Attorney/District Attorney Jack McCoy.

Law & Order's 24 seasons are second only to its spin off Law & Order: Special Victims Unit (1999–present) for the longest-running live action scripted American primetime series. The success of the series has led to the creation of additional shows, making Law & Order a franchise, including a television film, several video games, and international adaptations of the series. It has won and has been nominated for numerous awards over the years, including a number of Primetime Emmy Awards.

In 1988, Dick Wolf developed a concept for a new television series that was going to depict a relatively optimistic picture of the American criminal justice system. He initially toyed with the idea of calling it Night & Day but then hit upon the title Law & Order. The first half of each episode was going to follow two homicide detectives (a senior and a junior detective) and their commanding officer as they were investigating a violent crime.

The second half of the episode was going to follow the district attorney's office and the courts as two prosecutors, with advice from the district attorney, were attempting to convict the accused. Law & Order was going to be able to investigate some of the larger issues of the day by focusing on stories that were based on real cases making headlines.

Wolf took the idea to then-president of Universal Television Kerry McCluggage, who pointed out the similarity to a 1963 series titled Arrest and Trial, which lasted one season. The two watched the pilot of that series, in which a police officer (Ben Gazzara) arrested a man for armed robbery in the first half, and the defense attorney, played by Chuck Connors, gets the perpetrator off as the wrong guy in the second half; this was the formula of the show every week.