Porterbrook is a British rolling stock company (ROSCO), created as part of the privatisation of British Rail. Together with Angel Trains and Eversholt Rail Group, it is one of the three original ROSCOs.

The privatisation of British Rail was the process by which ownership and operation of the railways of Great Britain passed from government control into private hands. Begun in 1994, the process was largely completed by 1997. The deregulation of the industry was in part motivated by the enactment of EU Directive 91/440 in 1991, which aimed to create a more efficient railway network by creating greater competition.