A tower block, block of flats, or apartment block, is a multi-unit high-rise apartment building. In some areas they may be referred to as MDU standing for Multi Dwelling Unit.
Apartment blocks have technical and economic advantages in areas with high population density. They have become a distinguished form of housing accommodation in virtually all densely populated urban areas around the world. In contrast with low-rise and single-family houses, apartment blocks accommodate more inhabitants per unit of area of land they occupy and also decrease the cost of municipal infrastructure.

Apartment blocks around the world

United Kingdom
Tower blocks were first built in the UK after the Second World War, in many cases as a "quick-fix" to cure problems caused by crumbling and unsanitary 19th century dwellings or to replace buildings destroyed by German aerial bombing. Initially, they were welcomed, and their excellent views made them popular living places. Later, as the buildings themselves deteriorated, they grew a reputation for being undesirable low cost housing, and many tower blocks saw rising crime levels, increasing their unpopularity. One response to this was the great increase in the number of housing estates built, which in turn brings its own problems. In the UK, tower blocks particularly lost popularity after the partial collapse of Ronan Point in 1968. The city of Glasgow in Scotland contains the highest concentration of tower blocks in the UK - examples include the Hutchensontown C blocks in the Gorbals, the 20-storey blocks in Sighthill, and the 31-storey Red Road flats in the city's north east.
In recent years, some council or ex-council high-rises in the United Kingdom, including Trellick Tower, Keeling House and The Barbican Estate, have become popular with young professionals due to their excellent views, desirable locations and architectural pedigrees, and now command high prices. After a gap of around 30 years, new high-rise flats are once again being built in Birmingham, Glasgow, Leeds, Cardiff, Liverpool, London, and Manchester however this time for wealthy professionals. Their developers market these properties by using the American term 'apartment buildings', perhaps in an effort to distance these newer buildings from the older tower blocks from the 1950s and '60s.

United States
In the United States tower blocks are commonly referred to as midrise or highrise apartment buildings, depending on their height, while buildings that house fewer flats (apartments), or are not as tall as the tower blocks, are called lowrise apartment buildings.
Some of the first residential towers were the Castle Village towers in New York City completed in 1939. Their cross-shaped design was copied in towers in Parkchester and Stuyvesant Town residential developments.
The government's experiments in the 1960s and 70s to use high-rise apartments as a means of providing the housing solution for the poor resulted in a spectacular failure. All but a few high-rise housing projects in the nation's largest cities, such as Cabrini-Green and Robert Taylor Homes in Chicago, Penn South in New York and the Desire projects in New Orleans, fell victim to the "ghettofication" and are now being torn down, renovated, or replaced.
In contrast to their public housing cousins, commercially developed high-rise apartment buildings continue to flourish in cities around the country largely due to high land prices and the housing boom of the 2000s. The Upper East Side in New York City and Chicago's Gold Coast, both featuring high-rise apartments, are the wealthiest urban neighborhoods in the United States.

Ireland
Tower Blocks are Called Flats in Ireland. Most of the flats in the country are in Dublin, in such areas such as Ballymun, Dublin's north inner-city and Inchicore. Gang and Drug abuse problems are very common in these areas and other areas such as Summerhill, Fairview, Tallaght. Over the last five years the largest cities such as Dublin, Cork, Limerick and Galway have witnessed apartment building. Some large Towns such as Navan, Drogheda and Mullingar have also witnessed lots of apartments being built.

Eastern Europe and Russia
See also: Panelák and Plattenbau

Soviet housing

Post Cold-War buildup
Russia is currently undergoing a dramatic buildout, growing a commercially-shaped skyline that wasn't possible under communism.

Middle East