Quatermass (also known as Quatermass IV, or The Quatermass Conclusion for its intended international theatrical release) is a 1979 British television science fiction serial. Produced by Euston Films for Thames Television, it was broadcast on the ITV network in October and November 1979. Like its three predecessors, Quatermass was written by Nigel Kneale. It is the fourth and final television serial to feature the character of Professor Bernard Quatermass who was played by John Mills.

Influenced by the social and geopolitical situation of the early 1970s and the hippie youth movement of the late 1960s, Quatermass is set in a near future in which large numbers of young people are joining a cult known as the Planet People who gather at prehistoric sites, believing they will be transported to a better life on another planet. The series begins with Professor Quatermass arriving in London to look for his granddaughter, Hettie Carlson, and witnessing the destruction of two spacecraft and the disappearance of a group of Planet People at a stone circle by an unknown force. He investigates this force, believing that Hettie may be in danger. As the series progresses, it becomes apparent that the Planet People are being harvested by an alien force rather than transported.

Quatermass was originally conceived as a BBC production, but after the corporation lost faith in the project because of spiralling costs, work was halted. The scripts were acquired by Euston Films and Kneale, who was commissioned to rewrite the scripts into two versions: a four-part television serial and The Quatermass Conclusion, a 100-minute film, intended for international theatrical release.

Despite ITV making the series its flagship premier for its 1979 autumn schedule, the four-part serial was met with lukewarm reviews. Reasons were blamed on the plot, casting and character development. The cinematic edited version, The Quatermass Conclusion, was given a limited release due to lack of interest from distributors.