The 1953 Iranian coup d'état, known in Iran as the Mordad 28th coup d'état (Persian: کودتای ۲۸ مرداد), was the overthrow of Prime Minister Mohammad Mosaddegh on 19 August 1953. It was orchestrated by the United States (CIA) and the United Kingdom (MI6). A key motive was to protect British oil interests in Iran after Mossadegh nationalized and refused to concede to western oil demands. It was instigated by the United States (under the name TP-AJAX Project or Operation Ajax) and the United Kingdom (under the name Operation Boot).

Mosaddegh had sought to audit the documents of the Anglo-Iranian Oil Company (AIOC), a British corporation (now part of BP), to verify that AIOC was paying the contracted royalties to Iran, and to limit the company's control over Iranian oil reserves. Upon the AIOC's refusal to cooperate with the Iranian government, the parliament (Majlis) voted to nationalize Iran's oil industry and to expel foreign corporate representatives from the country. After this vote, Britain instigated a worldwide boycott of Iranian oil to pressure Iran economically. Initially, Britain mobilized its military to seize control of the British-built Abadan oil refinery, then the world's largest, but Prime Minister Clement Attlee (in power until 1951) opted instead to tighten the economic boycott while using Iranian agents to undermine Mosaddegh's government. Judging Mosaddegh to be unamenable and fearing the growing influence of the communist Tudeh, UK prime minister Winston Churchill and the Eisenhower administration decided in early 1953 to overthrow Iran's government. The preceding Truman administration had opposed a coup, fearing the precedent that Central Intelligence Agency (CIA) involvement would set, and the U.S. government had been considering unilateral action (without UK support) to assist the Mosaddegh government as late as 1952. British intelligence officials' conclusions and the UK government's solicitations to the US were instrumental in initiating and planning the coup.

Following the coup, a government under General Fazlollah Zahedi was formed which allowed Mohammad Reza Pahlavi, the shah of Iran (Persian for 'king'), to rule more firmly as monarch. He relied heavily on United States support to hold on to power. According to the CIA's declassified documents and records, some of the most feared mobsters in Tehran were hired by the CIA to stage pro-shah riots on 19 August. Other men paid by the CIA were brought into Tehran in buses and trucks and took over the streets of the city. Between 200 and 300 people were killed because of the conflict. Mosaddegh was arrested, tried and convicted of treason by the Shah's military court. On 21 December 1953, he was sentenced to three years in jail, then placed under house arrest for the remainder of his life. Other Mosaddegh supporters were imprisoned, and several received the death penalty. The coup strengthened the Shah's authority, and he continued to rule Iran for the next 26 years as a pro-Western monarch until he was overthrown in the Iranian Revolution in 1979.

In August 2013, the U.S. government formally acknowledged the U.S. role in the coup by releasing a bulk of previously classified government documents that show it was in charge of both the planning and the execution of the coup. According to American journalist Stephen Kinzer, the operation included false flag attacks, paid protesters, provocations, the bribing of Iranian politicians and high-ranking security and army officials, as well as pro-coup propaganda. The CIA is quoted as acknowledging the coup was carried out "under CIA direction" and "as an act of U.S. foreign policy, conceived and approved at the highest levels of government". In 2023, the CIA took credit for the coup, which some scholars disagreed with while others agreed that the U.S. and Britain had engineered the coup.

Throughout the 19th century, Iran was caught between two advancing imperial powers, Russia and Britain. In 1892, the British diplomat George Curzon described Iran as "pieces on a chessboard upon which is being played out a game for the dominion of the world." During the latter half of the 19th century, the concession policies of the monarchy faced increased opposition. In 1872, a representative of British entrepreneur Paul Reuter met with the Iranian monarch Naser al-Din Shah Qajar and agreed to fund the monarch's upcoming lavish visit to Europe in return for exclusive contracts for Iranian roads, telegraphs, mills, factories, extraction of resources, and other public works, in which Reuter would receive a stipulated sum for five years and 60% of all the net revenue for 20 years. However, the Reuter concession was never put into effect because of violent opposition at home and from Russia. In 1892 the Shah was forced to revoke a tobacco monopoly given to Major G. F. Talbot, following protests and a widespread tobacco boycott.

In 1901, Mozzafar al-Din Shah Qajar granted a 60-year petroleum search concession to William Knox D'Arcy. D'Arcy paid £20,000 (equivalent to £2.6 million in 2023), according to journalist-turned-historian Stephen Kinzer, and promised equal ownership shares, with 16% of any future net profit, as calculated by the company. However, the historian L. P. Elwell-Sutton wrote, in 1955, that "Persia's share was 'hardly spectacular' and no money changed hands." On 31 July 1907, D'Arcy withdrew from his private holdings in Persia, and transferred them to the British-owned Burmah Oil Company. On 26 May 1908 the company struck oil at a depth of 1,180 feet (360 m). The company grew slowly until World War I, when Persia's strategic importance led the British government to buy a controlling share in the company, essentially nationalizing British oil production in Iran.^{[citation needed]}

The British angered the Persians by intervening in their domestic affairs, including in the Persian Constitutional Revolution. Massive popular protests had forced Mozzafar al-Din Shah to allow for the Constitution of 1906, which limited his powers. It allowed for a parliament elected by the people to make the laws, and a prime minister to sign and carry them out. The prime minister would be confirmed by the shah after a vote in Parliament. Nevertheless, the new constitution gave the shah many executive powers as well. It allowed for the shah to issue royal decrees (Farman), gave him the power to dismiss prime ministers, appoint half of the members of the Senate (which was not convened until 1949), and introduce bills to dissolve Parliament. It abolished arbitrary rule, but the shah served as an executive, rather than in a ceremonial role. The Constitutional Revolution was opposed by the British and Russians, who attempted to subvert it through the backing of Mohammad Ali Shah Qajar (the son of Mozzafar-e-din Shah), who tried to break up the democratic government by force. A guerrilla movement led by Sattar Khan deposed him in 1910.

In the aftermath of World War I there was widespread political dissatisfaction with the royalty terms of the British petroleum concession, under the Anglo-Persian Oil Company (APOC), whereby Persia received 16% of "net profits". In 1921, after years of severe mismanagement under the Qajar dynasty, a coup d'état (allegedly backed by the British) brought a general, Reza Khan, into the government. By 1923, he had become prime minister, and gained a reputation as an effective politician with a lack of corruption.^{[page needed]} By 1925 under his influence, Parliament voted to remove Ahmad Shah Qajar from the throne, and Reza Khan was crowned Reza Shah Pahlavi, of the Pahlavi dynasty. Reza Shah began a rapid and successful modernization program in Persia, which up until that point had been considered to be among the most impoverished countries in the world. Nevertheless, Reza Shah was also a very harsh ruler who did not tolerate dissent. By the 1930s, he had suppressed all opposition, and had sidelined the democratic aspects of the constitution. Opponents were jailed and in some cases even executed. While some agreed with his policies, arguing that it was necessary as Iran was in such turmoil, others argued that it was unjustified.^{[page needed]} One such opponent was a politician named Mohammad Mosaddegh, who was jailed in 1940. The experience gave him a lasting dislike for authoritarian rule and monarchy, and it helped make Mosaddegh a dedicated advocate of complete oil nationalization in Iran.^{[page needed]}