Didcot is a major junction, where the (Great Western Railway-built) line to Oxford, and further north leaves the GWML to Bristol Temple Meads via Swindon, Chippenham and Bath Spa also to Swansea via and . There is no local service west of Didcot, so local service is exclusively provided by local trains taking the line to Oxford. However, a proportion of the main line services to Bristol and South Wales do stop here, with the remainder passing through the station non-stop. Fast trains to and from the Oxford line can avoid the station using the Didcot East curve.