Metroline, owned by ComfortDelGro Corporation of Singapore, is one of many companies operating bus services in London under the management of London Buses.

Metroline was founded in 1989 by London Buses Limited, privatised in 1994, and acquired by ComfortDelgro in 2000. It incorporates the Metroline London Northern subsidiary, which was acquired from MTL in 1998. It also bought Scottish Citylink in 1998. Between 2004 and 2005, Metroline stepped up its expansion drive, purchasing two smaller London bus operators, Armchair and Thorpes. The latter two companies continued to operate buses under their former names until 6 January 2007, when their bus operations merged with Metroline. It is the first operator to order Alexander Dennis Enviro400 buses, of which 28 entered service in early 2006 on cross-city route 24.

In 2005, Metroline was reported as the bus company with the second-most complaints filed with Transport for London, after Arriva London.

On 14 and 20 November 2006 Metroline bus drivers staged two one-day strikes over pay. It was the first London bus drivers strike of its kind in the 21st century. The dispute was successfully resolved between the company and trade union through further negotiation and compromise by both parties recommending an offer of 5.75% on all elements of pay. It was accepted by drivers in December 2006.