American late-night television news program that officially debuted on the American Broadcasting Company (ABC) network in 1980 and that began airing five nights per week in 1982. Through most of its life, it has been among the highest-profile and most influential television forums for discussion of the day's events.

Regarded as a broadcast news pioneer, the half-hour-long Nightline specializes in investigative journalism, in-depth and extended coverage of current events, and interviews with significant public figures. The program evolved from a 1979 nightly news special called The Iran Crisis: America Held Hostage, which became America's leading source for continued coverage of the Iran hostage crisis. Hosted by Ted Koppel, the show had strong viewership ratings in its time slot and carved out a unique late-night niche for hard news. In 1980 it was given a permanent time slot and renamed Nightline.

Unlike most other news programs, Nightline dedicates each episode to a single topic. The subject of one episode can vary widely from the next, but typical fare includes politics, economics, science, and breaking news. Year after year, Nightline delivers high-quality news coverage, including poignant and exclusive interviews with individuals such as former Chief Justice Warren Burger (Burger, Warren E.) and onetime Palestinian Liberation Organization leader Yāsir Arafāt (Arafāt, Yāsirʿ). The program and its staff earned major honours in broadcast journalism, among them many George Foster Peabody Awards for Broadcast Excellence (including a lifetime achievement award in 2002) and dozens of Emmys.

For 25 years Nightline was nearly synonymous with Koppel, one of America's most eminent broadcast journalists, who anchored the show from 1980 to 2005. Since Koppel's retirement, the show has been anchored by Cynthia McFadden, Terry Moran, and Martin Bashir.