West London is the western part of London, England, north of the River Thames, west of the City of London, and extending to the Greater London boundary.
The term is used to differentiate the area from the other parts of London: North London, East London and South London.  West London was part of the historic county of Middlesex.
Early West London had two main focuses of growth, the area around Thorney Island, site of Westminster Abbey and the Palace of Westminster, and ribbon development heading west - towards Westminster - from gates in the walls of the City of London. In the 17th century these areas of growth would be linked by high status new developments, which formed a focal point in their own right, later becoming known as the West End of London.
The development of the area began with the establishment of the Abbey on a site then called Thorney Island, the choice of site may in part relate to the natural ford which is thought to have carried Watling Street over the Thames in the vicinity.  Tradition dates the foundation to the 7th Century AD with written records dating back to the 960s or early 970s.  The Island and surrounding area became known as Westminster in reference to the church.
The legendary origin  is that in the early 7th century, a local fisherman named Edric ferried a stranger in tattered foreign clothing over the Thames to Thorney Island. It was a miraculous appearance of St Peter, a fisherman himself, coming to the island to consecrate the newly built church, which would subsequently develop into Westminster Abbey. He rewarded Edric with a bountiful catch when he next dropped his nets. Edric was instructed to present the King and St. Mellitus, Bishop of London with a salmon and various proofs that the consecration had already occurred . Every year on 29 June, St Peters day, the Worshipful Company of Fishmongers presents the Abbey with a salmon in memory of this event. 
The Palace of Westminster subsequently developed, with Parliament being based there from its establishment in 1265. The presence of the centre of government as a distinct focus for growth, accompanied by the proximity of the City, ensured that western London was the fastest growing part of early London.
The growth of the City of London beyond its city walls was much faster outside the western gates of Ludgate and Newgate than it was outside the gates to the north or to the east; this rapid growth was due to the roads from these western gates leading to the political centre of Westminster. The large and prosperous extra-mural ward of Farringdon Without, extensively urbanised during the 12th century, has been described as London's First West End. 
From the 15th to 17th centuries, growth along the roads from Ludgate (Fleet Street and The Strand) and Newgate (Holborn and High Holborn ) accelerated, and came to extend far beyond Farringdon Without, into Holborn, Bloomsbury and Westminster.
Urban growth extending from the Westminster urban area, linked up with that extending from the City in the time of Henry VIII. It was at around that time that Westminster first acquired City status. 
In the mid 17th century Henry Jermyn, was instrumental in developing the St James's and Mayfair districts of Westminster. These districts provided a fashionable new focus for western London, that came to be known as the West End. Jermyn would become known as the Father of the West End. 
In 1720, John Strype's "Survey of London" described Westminster as one of the then four distinct areas of London;  in it he describes the City of London, Westminster (West London), Southwark (South London), and 'That Part beyond the Tower' (East London). The area now usually referred to as North London developed later.
As well as the proximity of the centre of government, the West End was long favoured by the rich elite as a place of residence because it was usually upwind of the smoke drifting from the crowded City.  A further factor facilitating rapid growth in West London was the very large number of bridges linking the area to South London and the area beyond; by contrast, even today, there are no bridges east of Tower Bridge, partly as the river becomes wider as it heads east.
The term "West End of London" gained widespread currency as a proper noun, rather than just a geographical description in the 19th century.
Like other areas of the capital, West London grew rapidly in the Victorian era as a result of railway-based commuting; with the building of the termini at Paddington and Marylebone, and the lines radiating from them, having a particularly profound effect. This trend continued in the twentieth century and was subsequently reinforced by motorcar-based commuting.
The size of London stabilised after the establishment of the Metropolitan Green Belt shortly after the Second World War.
West London is an informally and inexactly defined area lying north of the River Thames and extends west from the edge of the City of London, to West London's historic and commercial core of Westminster and the West End, on to the Greater London boundary, much of which is formed by the River Colne. Some interpretations of the area include the boroughs of Brent and Harrow, taking ancient Watling Street as the boundary in those outer areas.  The Grand Union Canal is West London's major internal waterway.
West London is bordered by the administrative counties of Surrey to the south west and south; Berkshire to the west and north west; Buckinghamshire to the north west; and Hertfordshire to the north.
A publication by the Mayor of London in 2011 referred to the London boroughs of Brent, Harrow, Ealing, Hammersmith and Fulham, Hounslow, Richmond, and Hillingdon as West London. Some parts of West London, such as Westminster and the West End are also a part of Central London, an area which also lacks precise definition. The Royal Borough of Kingston upon Thames spans the River Thames so its status can be ambiguous.
The term West London is used to differentiate the area from other informal radial divisions of London, the Metropolitan Compass;  North London, East London and South London. 
The term "West London" has been used for a variety of formal purposes with the boundaries defined according to the purposes of the designation.
The 2011 iteration of the London Plan  included an altered "West" sub-region, to be used for planning, engagement, resource allocation and progress reporting purposes. It consists of the London Boroughs of Brent, Harrow, Ealing, Hammersmith and Fulham, Hillingdon, Hounslow and the Richmond upon Thames. As well as including outer areas of West London, the sub-region also includes areas south of the river, not usually counted as part of West London; areas of the cross-river London Borough of Richmond upon Thames.
The 2004-2008 and 2008-2011 versions of the sub-region varied in their composition.
The W (Western) postcode area was introduced in 1857  to facilitate the distribution of mail. The postcode area is a sub-set of West London.
The London Plan  defines two areas of London as International Centres, the West End and Knightsbridge, both in west London. Five of the thirteen Metropolitan Centres in the plan are also in West London: Ealing, Hounslow, Harrow, Uxbridge and Shepherd's Bush.
Eleven of the London Plan's thirty-eight Opportunity Areas are part of West London; Kensal Canalside, Paddington, Earl's Court and West Kensington, Harrow and Wealdstone, Park Royal, Old Oak Common, Southall, Tottenham Court Road, Victoria, Wembley and White City.
London Heathrow Airport is a major employer in West London, and the University of West London has more than 47,000 students. 
Westminster is an area of Central London, part of the wider City of Westminster.
The West End of London is a district of Central London, west of the City of London and north of the River Thames, in which many of the city's major tourist attractions, shops, businesses, government buildings and entertainment venues, including West End theatres, are concentrated.
Hounslow is a large suburban district of West London, 10+3⁄4 miles west-southwest of Charing Cross. It is the administrative centre of the London Borough of Hounslow, and is identified in the London Plan as one of the 12 metropolitan centres in Greater London.
The London Borough of Hounslow is a London borough in West London, England, forming part of Outer London. It was created in 1965 when three smaller borough councils amalgamated under the London Government Act 1963. It is governed by Hounslow London Borough Council.
Holborn is a district in central London, which covers the south-eastern part of the London Borough of Camden and a part of the Ward of Farringdon Without in the City of London.
The London postal district is the area in England of 241 square miles (620 km2) to which mail addressed to the London post town is delivered. The General Post Office under the control of the Postmaster General directed Sir Rowland Hill to devise the area in 1856 and throughout its history it has been subject to reorganisation and division into increasingly smaller postal units, with the early loss of two compass points and a minor retraction in 1866. It was integrated by the Post Office into the national postcode system of the United Kingdom during the early 1970s and corresponds to the E, EC, N, NW, SE, SW, W and WC postcode areas. The postal district has also been known as the London postal area. The County of London was much smaller, at 117 square miles (300 km2), but Greater London is much larger at 607 square miles (1,570 km2).
Middlesex was a historic county in southeast England. Its area was almost entirely within the wider urbanised area of London and mostly within the ceremonial county of Greater London, with small sections in neighbouring ceremonial counties. Three rivers provide most of the county's boundaries; the Thames in the south, the Lea to the east and the Colne to the west. A line of hills forms the northern boundary with Hertfordshire.
South London is the southern part of London, England, south of the River Thames. The region consists of the boroughs, in whole or in part, of Bexley, Bromley, Croydon, Greenwich, Kingston, Lambeth, Lewisham, Merton, Richmond, Southwark, Sutton and Wandsworth.
The Metropolitan District Railway, also known as the District Railway, was a passenger railway that served London from 1868 to 1933. Established in 1864 to complete an "inner circle" of lines connecting railway termini in London, the first part of the line opened using gas-lit wooden carriages hauled by steam locomotives. The Metropolitan Railway operated all services until the District Railway introduced its own trains in 1871. The railway was soon extended westwards through Earl's Court to Fulham, Richmond, Ealing and Hounslow. After completing the inner circle and reaching Whitechapel in 1884, it was extended to Upminster in Essex in 1902.
East London is the northeastern part of London, United Kingdom. Located east of the ancient City of London and north of the River Thames as it begins to widen, East London developed as London's docklands and the primary industrial centre. The expansion of railways in the 19th century encouraged the eastward expansion of the East End of London and a proliferation of new suburbs. The industrial lands of East London are today an area of regeneration, which are well advanced in places such as Canary Wharf and ongoing elsewhere.
The WC postcode area, also known as the London WC postcode area, is a group of postcode districts in central London, England. The area covered is of high density development, and includes parts of the City of Westminster and the London Boroughs of Camden and Islington, plus a very small part of the City of London.
The TW postcode area, also known as the Twickenham postcode area, is a group of twenty postcode districts in south-east England, within thirteen post towns. These cover parts of south-west London and north-west Surrey, plus a very small part of Berkshire.
The region of Greater London, including the City of London, is divided into 73 parliamentary constituencies which are sub-classified as borough constituencies, affecting the type of electoral officer and level of expenses permitted.
The River Crane, a tributary of the River Thames, runs 8.5 miles (13.6 km) in West London, England. It forms the lower course of Yeading Brook. It adjoins or passes through three London boroughs: Hillingdon, Hounslow and Richmond upon Thames, in the historic county of Middlesex. The drainage basin is heavily urbanised but many of the Hayes to Whitton flood-meadows have been conserved, forming a narrow, green vale, opening out to what remains of Hounslow Heath in the centre – a near-continuous belt of semi-natural habitat.
The Greater London Built-up Area, or Greater London Urban Area, is a conurbation in south-east England that constitutes the continuous urban sprawl of London, and includes surrounding adjacent urban towns as defined by the Office for National Statistics. It is the largest urban area in the United Kingdom with a population of 9,787,426 in 2011.
London has centres of worship for a multitude of faiths. According to the 2011 Census, the largest religious groupings are Christians, followed by those of no religion, Muslims, no response ,Hindus, Jews, Sikhs, Buddhists and other.
The following outline is provided as an overview of and topical guide to London: