An Unearthly Child (sometimes referred to as 100,000 BC) is the first serial of the British science fiction television series Doctor Who. It was first broadcast on BBC TV in four weekly parts from 23 November to 14 December 1963. Scripted by Australian writer Anthony Coburn, the serial introduces William Hartnell as the First Doctor and his original companions: Carole Ann Ford as the Doctor's granddaughter, Susan Foreman, with Jacqueline Hill and William Russell as school teachers Barbara Wright and Ian Chesterton. The first episode deals with Ian and Barbara's discovery of the Doctor and his time-space ship, the TARDIS, in a junkyard in contemporary London. The remaining episodes are set amid a power struggle between warring Stone Age factions who have lost the secret of making fire.

The show was created to fill a gap between children's and young adult programming. Canadian producer Sydney Newman, recently made Head of Drama at the BBC, was tasked with creating the show, with heavy contributions from Donald Wilson and C. E. Webber. Newman conceived the idea of the TARDIS, as well as the central character of the Doctor. Production was led by Verity Lambert, the BBC drama department's first female producer, and the serial was directed by Waris Hussein. Following several delays, the first episode was recorded in September 1963 on 405-line black and white videotape, but was re-recorded the following month due to several technical and performance errors. Several changes were made to the show's costuming, effects, performances, and scripts throughout production.

The show's launch was overshadowed by the assassination of American President John F. Kennedy the previous day, resulting in a repeat of the first episode the following week. The serial received mixed reviews, and the four episodes attracted an average of six million viewers. Retrospective reviews of the serial are favourable. It later received several print adaptations and home media releases.