The Bombardier Turbostar is a family of diesel multiple unit (DMU) passenger trains that was built by ADtranz and later Bombardier Transportation at Derby Litchurch Lane Works in the United Kingdom between 1997 and 2011. The Turbostar was the first new train type to be introduced after the privatisation of British Rail. The first units were ordered by Chiltern Railways in 1996 and were designated Class 168. Since then the family has grown with the addition of the Class 170, Class 171, and the Class 172.

A diesel multiple unit or DMU is a multiple-unit train powered by on-board diesel engines. A DMU requires no separate locomotive, as the engines are incorporated into one or more of the carriages. Diesel-powered single-unit railcars are also generally classed as DMUs. Diesel-powered units may be further classified by their transmission type: diesel–mechanical DMMU, diesel–hydraulic DHMU, or diesel–electric DEMU.