The International Monetary Fund (IMF) is an international financial institution and a specialized agency of the United Nations, headquartered in Washington, D.C. It consists of 191 member countries, and its stated mission is "working to foster global monetary cooperation, secure financial stability, facilitate international trade, promote high employment and sustainable economic growth, and reduce poverty around the world". The IMF acts as a lender of last resort to its members experiencing actual or potential balance of payments crises.

Established in July 1944 at the Bretton Woods Conference based on the ideas of Harry Dexter White and John Maynard Keynes, the IMF came into formal existence in 1945 with 29 member countries and the goal of reconstructing the international monetary system. For its first three decades, the IMF oversaw the Bretton Woods system of fixed exchange rate arrangements. Following the collapse of this system in 1971, the Fund's role shifted to managing balance-of-payments difficulties and international financial crises, becoming a key institution in the era of globalization.

Through a quota system, countries contribute funds to a pool from which they can borrow if they experience balance-of-payments problems; a country's quota also determines its voting power. As a condition for loans, the IMF often requires borrowing countries to undertake policy reforms, known as structural adjustment. The organization also provides technical assistance and economic surveillance of its members' economies.

The IMF was originally laid out as a part of the Bretton Woods system exchange agreement in the year 1944. During the Great Depression, countries sharply raised barriers to trade in an attempt to improve their failing economies. This led to the devaluation of national currencies and a decline in world trade.

This breakdown in international monetary cooperation created a need for oversight. The representatives of 45 governments met at the Bretton Woods Conference in the Mount Washington Hotel in Bretton Woods, New Hampshire, in the United States, to discuss a framework for postwar international economic cooperation and how to rebuild Europe.

There were two views on the role the IMF should assume as a global economic institution. American delegate Harry Dexter White foresaw an IMF that functioned more like a bank, making sure that borrowing states could repay their debts on time. Most of White's plan was incorporated into the final acts adopted at Bretton Woods. British economist John Maynard Keynes, on the other hand, imagined that the IMF would be a cooperative fund upon which member states could draw to maintain economic activity and employment through periodic crises.

This view suggested an IMF that helped governments and act as the United States government had during the New Deal to the great depression of the 1930s.

The IMF provided two major lending packages in the early 2000s to Argentina (during the 1998–2002 Argentine great depression) and Uruguay (after the 2002 Uruguay banking crisis). However, by the mid-2000s, IMF lending was at its lowest share of world GDP since the 1970s.

In May 2010, the IMF participated, in 3:11 proportion, in the first Greek bailout that totaled €110 billion, to address the great accumulation of public debt, caused by continuing large public sector deficits. As part of the bailout, the Greek government agreed to adopt austerity measures that would reduce the deficit from 11% in 2009 to "well below 3%" in 2014.

The bailout did not include debt restructuring measures such as a haircut, to the chagrin of the Swiss, Brazilian, Indian, Russian, and Argentinian Directors of the IMF, with the Greek authorities themselves (at the time, PM George Papandreou and Finance Minister Giorgos Papakonstantinou) ruling out a haircut.

A second bailout package of more than €100 billion was agreed upon over the course of a few months from October 2011, during which time Papandreou was forced from office. The so-called Troika, of which the IMF is part, are joint managers of this programme, which was approved by the executive directors of the IMF on 15 March 2012 for XDR 23.8 billion and saw private bondholders take a haircut of upwards of 50%. In the interval between May 2010 and February 2012 the private banks of Holland, France, and Germany reduced exposure to Greek debt from €122 billion to €66 billion.

Not all member countries of the IMF are sovereign states, and therefore not all "member countries" of the IMF are members of the United Nations. Amidst "member countries" of the IMF that are not member states of the UN are non-sovereign areas with special jurisdictions that are officially under the sovereignty of full UN member states, such as Aruba, Curaçao, Hong Kong, and Macao, as well as Kosovo. The corporate members appoint ex-officio voting members, who are listed below. All members of the IMF are also International Bank for Reconstruction and Development (IBRD) members and vice versa.

Former members are Cuba (which left in 1964), and Taiwan, which was ejected from the IMF in 1980 after losing the support of the then United States President Jimmy Carter and was replaced by the People's Republic of China. However, "Taiwan Province of China" is still listed in the official IMF indices. Poland withdrew in 1950—allegedly pressured by the Soviet Union—but returned in 1986. The former Czechoslovakia was expelled in 1954 for "failing to provide required data" and was readmitted in 1990, after the Velvet Revolution.

Apart from Cuba, the other UN states that do not belong to the IMF are Monaco and North Korea. Liechtenstein became the 191st member on 21 October 2024.

Any country may apply to be a part of the IMF. Post-IMF formation, in the early postwar period, rules for IMF membership were left relatively loose. Members needed to make periodic membership payments towards their quota, to refrain from currency restrictions unless granted IMF permission, to abide by the Code of Conduct in the IMF Articles of Agreement, and to provide national economic information. However, stricter rules were imposed on governments that applied to the IMF for funding.

The countries that joined the IMF between 1945 and 1971 agreed to keep their exchange rates secured at rates that could be adjusted only to correct a "fundamental disequilibrium" in the balance of payments, and only with the IMF's agreement.