The British Rail Class 777 METRO is a class of electric multiple unit passenger trains currently being delivered by the Swiss rolling stock manufacturer Stadler Rail, being used on the Merseyrail network in the Liverpool City Region and adjacent areas of Cheshire and Lancashire. The trains have the ability to operate on the third rail-powered sections of the network, with some units carrying onboard batteries to allow use on unpowered track. Ordered in 2016, construction of the units began in 2018. The first unit entered service on 23 January 2023, following delays to the deployment programme. The Class 777 will replace Merseyrail's current Class 507 and Class 508 units, which were built between 1978 and 1980. Seven units of the total 53 ordered are being configured as battery electric multiple units (BEMUs) for use on non-electrified lines, being designated subclass 777/1.

Stadler Rail is a Swiss manufacturer of railway rolling stock, with an original emphasis on regional train multiple units and trams, but moving also into underground, high speed, intercity and sleeper trains. It is also producing niche products, such as being one of the last European manufacturers of rack railway rolling stock. Stadler Rail is headquartered at its place of origin in Bussnang, Switzerland. Stadler Rail employed 13,400 employees by 2022.