The First 48 is an American reality television show based on homicide detective units in various cities across the United States, including Philadelphia, Pennsylvania; Cincinnati, Ohio; Dallas, Texas; Detroit, Michigan; Kansas City, Missouri; Kansas City, Kansas; Memphis, Tennessee; Phoenix, Arizona; Las Vegas, Nevada; and Miami, Florida.

The show's premise is summarized in the title voice over: "For homicide detectives, the clock starts ticking the moment they are called. Their chance of solving a case is cut in half if they don't get a lead in the first 48 [hours]." A countdown timer is shown occasionally during the show to reinforce this, and to add drama.

Each episode picks one or two homicides in different cities (though in early episodes, both are in the same city), covering each alternately, showing how the detectives follow leads, use the media, investigate evidence forensically, and use their wits to catch the suspects.

The First 48 is notable because it takes viewers behind the scenes of real-life investigations with unprecedented access to crime scenes, autopsies, forensic processing, and interrogations, offering a view of homicide detective work that is not obscured by the veil of fiction. The original soundtrack, composed by Chuck Hammer, is a combination of dark ambient music integrated with sound design.

The show offers a realistic, uncompromising, gritty view of homicide detectives in America, and the methods they use to do their job effectively. It has been noted that a great majority of suspects are either Black or hispanic, indicating a possible bias. However, it is important to point out that most inner-city homicides are related to poverty, which affects these communities profoundly.