East London is the part of London, England, 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 East End of London, the old core of modern East London, began with the medieval growth of London beyond the city walls, along the Roman roads leading from Bishopsgate and Aldgate, and also along the river. The initially modest eastern extensions were separated from the northern and western suburbs by the marshy open area of Moorfields adjacent to the wall on the north side, which discouraged development in that direction. Building accelerated in the late 16th century, and the area that would later become known as the East End began to take shape.

In 1720 John Strype described London as consisting of four main parts; The City of London, Westminster, Southwark and That Part Beyond the Tower. This was the first time that East London was explicitly recognised as one of the capital's major quarters.

The relevance of Strype's reference to the Tower of London was more than geographical. The East End was the urbanised part of an administrative area called the Tower Division (also known as the Tower Hamlets), which had owed military service to the Constable of the Tower (in his ex-officio role as Lord Lieutenant of the Tower Hamlets) from an unknown point in the medieval period, having its roots in the Bishop of London's historic Manor of Stepney. This made the Constable a prominent figure in the civil and military affairs of the East End.

Growth was stimulated by the maritime trades (such as shipbuilding and dockyards) along the River Thames, with weaving a major employer inland, and many factories sprung up on either bank of the River Lea. These factories accelerated the growth of new suburbs beginning in West Ham, that lay east of Bow Bridge, and the Lea, in Essex. This growth was given further impetus by the opening of the Royal Victoria Dock in 1855.

The growth of population in the parishes to the east of the City of London led to a need to break up the ancient parish of Stepney into smaller units to provide adequate religious and civil administration. The existing administrative framework was supplemented by the Metropolitan Board of Works between 1856 and 1889. This covered much of the capital but excluded the area east of the Lea.

The Tower Division continued to operate as a county and hundred until replaced by the new Metropolitan Boroughs of Stepney, Shoreditch, Hackney, Poplar and Bethnal Green, in the new County of London, in local government re-organisations of 1890 and 1900. These boroughs would be replaced by larger new London Boroughs in 1965.

The majority of the rail network in East London was built within fifty years from 1839. The first through the area was the Eastern Counties Railway from Mile End to Romford, extended to Shoreditch in 1840. The London and Blackwall Railway built a line from Minories to Blackwall the same year and the Northern and Eastern Railway connected Lea Bridge and Tottenham with the Eastern Counties at Stratford. The Eastern Counties and Thames Junction Railway started passenger service on their line from Stratford to Canning Town, Custom House and North Woolwich in 1847. This made Stratford a significant railway junction and location of railway works. The East & West India Docks & Birmingham Junction Railway connected Kingsland with Bow and Poplar in 1850 and was renamed North London Railway in 1853.