Countdown was a British comic published weekly by Polystyle Publications – ultimately, under several different titles – from early 1971 to late summer 1973. The pages in each issue were numbered in reverse order, with page 1 at the end – a gimmick which was derived from the comic's title in order to create a countdown to the number one every week.

Countdown initially featured many comic strips based on Gerry Anderson's Supermarionation TV shows which had been popular throughout the 1960s. (Much of this material was reprinted from an earlier publication called TV Century 21.) The principle exceptions to this were the Doctor Who strip, which had previously appeared in Polystyle's long-established title TV Comic, the Anderson's new live-action series UFO, and (from issue 35) the Roger Moore/Tony Curtis vehicle The Persuaders!.

It was a high-quality (but expensive) publication, featuring full-colour art on the cover and on many of the inside pages, and was printed on coated paper. After 58 weeks, the publisher cut costs by relaunching the comic under the title TV Action, in a much cheaper format. The relaunch saw a shift in emphasis away from Gerry Anderson content, instead focusing on comic strip stories based on popular crime and adventure TV series of the era.

A notable feature of Countdown was the inclusion of nonfiction articles about current space exploration which often included a level of technical detail more typical of technical trade journals aimed at adult professionals.