Whoever wins the election to be London's next mayor will inherit a budget of almost £20bn and wide-ranging powers over transport, policing and regeneration.
The mayor controls Transport for London which runs buses, trams, the Tube, London Overground, Docklands Light Railway as well as licensing taxi and minicab drivers.
The mayor has power to set ticket prices on buses and trams as well as some, but not all, Tube and train services.
TfL also collects income from the central London Congestion Charge and the Ultra-Low Emission Zone and operates bus and bike lanes on some main roads.
The troubled Crossrail project, delayed by at least three years and £4bn over budget also comes under the mayor's TfL umbrella.
The mayor is London's defacto police and crime commissioner and oversees police spending as well as dictating the capital's policing strategy through a police and crime plan.
The Metropolitan Police Service £4bn budget includes £766m raised by the mayor from London council taxpayers.
The mayor has a shared responsibility with the Home Secretary for hiring and firing the MPS commissioner.
City Hall has similar oversight of London Fire Brigade and the ability to hire and fire the LFB commissioner.
Housing strategy is another mayoral responsibility. The mayor's London plan identified a need for 49,000 new homes every year. The government has given the mayor £4.8bn to spend on affordable housing.
The mayor also controls two 'regeneration' agencies. The London Legacy Development Corporation was set up to oversee the transformation of the 2012 Olympic Park in Stratford.
The Old Oak and Park Royal Development Corporation is focussed on land around the planned HS2 railway station at Old Oak Common.