Chiltern Railways is a British train operating company owned by Arriva UK Trains that has operated the Chiltern Railways franchise since July 1996. It operates commuter/regional rail passenger services from its central London terminus at London Marylebone along the M40 corridor to destinations in Buckinghamshire, Oxfordshire and Warwickshire, as well as long-distance services to the West Midlands along two routes. Services on the Chiltern Main Line run from London to Birmingham Snow Hill, Stratford-upon-Avon and Oxford, with some peak-hour services extended to Kidderminster.

Chiltern Railways also runs trains on the London–Aylesbury line to Aylesbury (some of which continue on to Aylesbury Vale Parkway), and on the Princes Risborough to Aylesbury and Oxford to Bicester branch lines.