The Class 377 Electrostar is a British electric multiple-unit train (EMU) built by Bombardier Transportation at its Derby Works, from 2001 to the present. The Electrostar family is the most numerous type of EMU built in the post-privatisation period of Britain's railways. The class forms the major part of the Govia Thameslink Railway (GTR) fleet for Southern and Thameslink services. They are primarily seen on services in the south of England.