One (stylized as one) is a German free-to-air television channel owned and operated by the German public-broadcasting consortium ARD. Managed since October 2005 by Westdeutscher Rundfunk on behalf of ARD as a whole, the channel was launched (as EinsFestival) on 30 August 1997.

On 29 July 2016, WDR announced that from early September 2016 Einsfestival became One and became a channel specifically aimed at viewers aged between 30 and 49. The channel's website, Twitter, and Facebook presences were updated on 1 September 2016, and the on-air rebrand took effect on 3 September 2016, starting with adoption of the new screen identification at 0.00 and ending with the final adjustment of all aspects of the channel's visual design at 10.00.

The rebrand was aimed at increasing awareness of the station as an entertainment channel, particularly among viewers under 30.

On 15 November 2022, One closed its SDTV feed across its cable and satellite feeds, which means it is now only available in HD.

One concentrates on entertainment, and the channel's content is very largely made up of repeat broadcasts of programmes already shown on other ARD channels, national and regional: this includes cinema and television films, drama series, documentaries, reports, magazines, and music programmes (especially rock and pop).

Since the 2004 Summer Olympics ARD and ZDF have used their digital television channels (respectively, One and ZDFneo) to broadcast additional coverage of such sporting events as the Olympic Games and the UEFA European Football Championship. For example, during UEFA Euro 2008 and the 2010 FIFA World Cup these digital channels were used to provide coverage of different matches taking place simultaneously.

One also carries the semi-finals of the Eurovision Song Contest, as well as the final (which is also broadcast by ARD's principal channel, Das Erste).

SD broadcasting via satellite (Astra 19.2) stopped on 12 January 2021.