The Great Western and Great Central Joint Railway was a railway built and operated jointly by the Great Western Railway (GWR) and Great Central Railway (GCR) between Northolt (in north west London) and Ashendon Junction (west of Aylesbury). It was laid out as a trunk route with gentle curves and gradients and spacious track layouts. The two companies each needed approach railways at both ends of the line to connect their respective systems; these were built as part of a single project.
The joint line opened in 1905 and gave the GCR a better route than previously for its London Extension from Nottingham and Leicester. When the GWR completed its "Bicester Cut-off", combined with the Joint Line itself the GWR had a much shorter and better route for its Birmingham and Birkenhead traffic.
Most of the GCR's London Extension was closed in 1966 but the Joint Line, the GCR approach through Wembley and the GWR Bicester Cut-off are still in use as a secondary main line from London to Birmingham, in intensive use by Chiltern Railways.