National Westminster Bank, commonly known as NatWest, is a major retail and commercial bank in the United Kingdom based in London, England. It was established in 1968 by the merger of National Provincial Bank and Westminster Bank. In 2000, it became part of The Royal Bank of Scotland Group, which was re-named NatWest Group in 2020. Following ringfencing of the group's core domestic business, the bank became a direct subsidiary of NatWest Holdings; NatWest Markets comprises the non-ringfenced investment banking arm. NatWest International is a trading name of RBS International, which also sits outside the ringfence.

Between 2008 and 2025, the UK government held a stake in NatWest Group following its £45 billion ($61.87 billion) bailout of the lender which led to it owning 84 per cent at one point. The bank returned to full private ownership on 30 May 2025 after 17 years.

NatWest is considered one of the Big Four clearing banks in the UK, and it has a large network of over 526 branches and 3,400 cash machines across Great Britain and offers 24-hour Actionline telephone and online banking services. Today, it has more than 7.5 million personal customers and 850,000 small business accounts. In Northern Ireland, it operates through the Ulster Bank brand.

The bank's origins date back to 1658 with the foundation of Smith's Bank of Nottingham. Its oldest direct corporate ancestor, National Provincial Bank, was formed in 1833 as the National Provincial Bank of England. It merged with Union of London and Smith's Bank in 1918 to become National Provincial and Union Bank, shortening its name in 1924. District Bank (formed in 1829 as the Manchester and Liverpool District Banking Company) was acquired by National Provincial in 1962 and allowed to operate under its own name. Westminster Bank was formed in 1834 as London and Westminster Bank. It merged with London and County Bank in 1909 to become London County and Westminster Bank and with Parr's Bank in 1918 to become London County Westminster and Parrs Bank, shortening its name in 1923.

The creation of the modern bank was announced in 1968 and commenced trading on 1 January 1970 after the statutory process of integration had been completed in 1969. The three arrowheads device was adopted as the new bank's logo; it is said to symbolise either the circulation of money in the financial system or the bank's three constituents. The District, National Provincial and Westminster banks were fully integrated in the new firm's structure, but private bankers Coutts & Co (a 1920 National Provincial acquisition, established 1692), Ulster Bank in Northern Ireland (a 1917 Westminster acquisition, established 1836) and the Isle of Man Bank (a 1961 National Provincial acquisition, established 1865) continued as separate operations. Westminster Foreign Bank (established 1913) was restyled International Westminster Bank in 1973. Duncan Stirling, outgoing chairman of Westminster Bank, became first chairman of the fifth-largest bank in the world. In 1969 David Robarts, former chairman of National Provincial, assumed Stirling's position. In 1975 it was one of the first London banks to open a representative office in Scotland. It was a founder member of the Joint Credit Card Company (with Lloyds Bank, Midland Bank and Williams & Glyn's Bank) which launched the Access credit card (now part of Mastercard) in 1972 and in 1976 it introduced the Servicetill cash machine. The same banks, excluding Lloyds, were later responsible for the introduction of the Switch debit card (later branded Maestro) in 1988.

Deregulation in the 1980s, culminating in the Big Bang in 1986, also encouraged the bank to enter the securities business. County Bank, its merchant banking subsidiary formed in 1965, acquired various stockbroking and jobbing firms to create the investment banking arm County NatWest. National Westminster Home Loans was established in 1980 and other initiatives included the launch of the Piggy Account for children in 1983, the Credit Zone, a flexible overdraft facility on which customers only pay interest (now commonplace, this so-called pink debt was innovative when launched) and the development of the Mondex electronic purse (later sold to MasterCard Worldwide) in 1990. The Action Bank advertising campaign spearheaded a new marketing-led approach to business development. Under the direction of Robin Leigh-Pemberton, who became chairman in 1977, the bank also expanded internationally, forming National Westminster Bancorp in the United States of America with a network of 340 branches across two states, National Westminster Bank of Canada and NatWest Australia Bank; and opening branches on the European continent and in the Far East. In 1982, the Frankfurt office of International Westminster Bank merged with Global Bank AG to form Deutsche Westminster Bank. In 1985, Banco NatWest España was formed and National Westminster Bank SA was incorporated in 1988, taking over the bank's six branches in France and Monaco. In 1989, International Westminster Bank was merged into National Westminster Bank by Act of Parliament.

Completed in 1980, the bank built the National Westminster Tower (now known as Tower 42) in London to serve as its international headquarters. At a height of 600 feet (183 m) it was the tallest building in the UK until the topping-out of Canary Wharf Tower 10 years later; its footprint loosely approximating the bank's logo when viewed from the air, although the architect claimed the similarity was coincidence. Also worthy of note is National Westminster House (since renamed as 103 Colmore Row) in Birmingham: the building was sold to British Land in 2007 and demolished in 2015.

The bank was hit by the stock market crash of 1987 and involvement in the collapse of Blue Arrow. The Department of Trade and Industry report on the affair was critical of the bank's management and resulted in the resignation of several members of the board, including then-chairman Lord Boardman. Later, the bank would divest its overseas subsidiaries. The North American operations were sold to Fleet Bank and Hong Kong Bank of Canada, and the Australian and New Zealand branches were sold to Salomon Smith Barney and the National Australia Bank. Thereafter the bank concentrated on its core domestic business as the restyled NatWest Group, reflecting its modern positioning as a portfolio of businesses. In the 1993 Bishopsgate bombing, the NatWest Tower was devastated by a Provisional IRA bomb and the bank vacated the building and later sold it. Then, in 1997, NatWest Markets, the corporate and investment banking arm formed in 1992, revealed that a £50 million ($67.75 million) loss had been discovered, revised to £90.5  million ($122.62 million) after further investigations. Investor and shareholder confidence was so badly shaken that the Bank of England had to instruct the board of directors to resist calls for the resignation of its most senior executives in an effort to draw a line under the affair. The bank's internal controls and risk management were severely criticised in 2000 and its aggressive push into investment banking questioned, after a lengthy investigation by the Securities and Futures Authority. The bank's move into complicated derivative products that it did not fully understand seemed to indicate poor management. By the end of 1997 parts of NatWest Markets had been sold, others becoming Greenwich NatWest in 1998. It had purchased Gleacher Partners in 1996 for $135 million only to resell it back to GP's founder for just $4 million 3 years later in 1999.