The Ariel 5 joint U.K./U.S. programme is described from its inception in 1967 through its various phases and including the multi-national launch operations from Kenya to the very successful post-launch operations now being conducted. The project organization is detailed and also the arrangements made for satellite control and data processing. A brief description of the on-board systems has been made together with a reference to their in-orbit performance. The broad objectives of the satellite and the main features of the experiments are outlined to give an overall background to the scientific capability of Ariel 5. A short account is given of the observing programme, together with a list of the regions of sky studied by the pointing experiments in the first year of operation.