Sirima Ratwatte Dias Bandaranaike (Sinhala: ; Tamil: ; 17 April 1916 10 October 2000), commonly known as Sirimavo Bandaranaike, was a Sri Lankan politician. She was the world's first female prime minister, when she became Prime Minister of Sri Lanka (then the Dominion of Ceylon) in 1960. She chaired the Sri Lanka Freedom Party from 1960 to 1994 and served three terms as prime minister, two times as the chief executive, 1960 to 1965 and 1970 to 1977, and once again in a presidential system from 1994 to 2000, governing under the presidency of her daughter Chandrika Kumaratunga.

Born into a Sinhalese Kandyan aristocratic family, Bandaranaike was educated in Catholic, English-medium schools, but remained a Buddhist and spoke Sinhala as well as English. On graduating from secondary school, she worked for various social programmes before marrying and raising a family. Playing hostess to her husband S. W. R. D. Bandaranaike, who founded the socialist Sri Lanka Freedom Party in 1951 and became prime minister in 1956, she gained his trust as an informal advisor. Her social work focused on improving the lives of women and girls in rural areas of Sri Lanka. Following her husband's assassination in 1959, Bandaranaike was soon persuaded by the party leadership during a brief time in opposition to enter politics herself and succeed her husband as chairwoman; she returned her party to the government and defeated prime minister Dudley Senanayake's UNP in the July 1960 election. She was then unseated by Senanayake in the 1965 election and became Leader of the Opposition, before winning a large majority in 1970 due to a cleverly structured election alliance with rival Marxist parties.

Bandaranaike attempted to reform the former British colony of Ceylon into a socialist republic by nationalising organisations in the banking, education, industry, media and trade sectors. Changing the administrative language from English to Sinhala and routinely campaigning on Sinhalese nationalist and anti-Tamil policies, which was political mainstream, she exacerbated discontent among the native Tamil population, and with the estate Tamils, who had become stateless under the Citizenship Act of 1948. During Bandaranaike's first two terms as prime minister, the country was plagued by high inflation and taxes, a dependence on food imports to feed the populace, high unemployment, and polarisation between the Sinhalese and Tamil populations because of her Sinhalese nationalist policies. Surviving an attempted coup d'tat in 1962, as well as a 1971 insurrection of radical youths, in 1972 she oversaw the drafting of a new constitution and the formation of the Sri Lankan republic, seperating it from the British Empire and also extending the parliamentary period until 1977. In 1975, Bandaranaike created what would eventually become the Sri Lankan Ministry of Women and Child Affairs, also appointing the first woman to serve in the Sri Lankan Cabinet aside from herself. Bandaranaike's tenure was marked by inadequate economic development at the national level. She played a large role abroad as a negotiator and a leader among the Non-Aligned Nations.

Losing against J. R. Jayewardene in a colossal landslide in the 1977 election and as the UNP government greatly reduced democratic rights, Bandaranaike was stripped of her civil rights in 1980 for claimed abuses of power during her tenure and barred from government for seven years, making her uneligible for the 1982 presidential election in the new presidential system. The new government initially improved the domestic economy, but failed to address social issues, and led the country into a protracted civil war against Tamil militants, which escelated in brutality over the years, especially when the Indian Peace Keeping Force was allowed to intervene. When she was allowed to return as a public figure in 1986, Bandaranaike opposed the Indian intervention, believing it violated Sri Lankan sovereignty. Failing to win the office of President against new UNP leader Ranasinghe Premadasa in 1988, she restored her party, which had by now developed more centrist policies and advocated for a reconcilliatory approach towards Tamils in the civil war, as a relevant force in the first parliamentary election after 12 years and served a second time as Leader of the Opposition from 1989 to 1994. When her daughter, who succeeded her as party leader, won the 1994 presidential election, Bandaranaike was appointed to her third term as prime minister and served until her retirement in 2000, two months prior to her death.

Sri Lanka (UK: , US: (listen); Sinhala: ශ්‍රී ලංකාව, romanized: Śrī Laṅkā (IPA: [ʃriː laŋkaː]); Tamil: இலங்கை, romanized: Ilaṅkai (IPA: [ilaŋɡaj])), formerly known as Ceylon, and officially the Democratic Socialist Republic of Sri Lanka, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, and southeast of the Arabian Sea; it is separated from the Indian subcontinent by the Gulf of Mannar and the Palk Strait. Sri Lanka shares a maritime border with India and the Maldives. Sri Jayawardenepura Kotte is its legislative capital, and Colombo is its largest city and financial centre.

Sri Lanka's documented history goes back 3,000 years, with evidence of prehistoric human settlements that dates to at least 125,000 years ago. It has a rich cultural heritage. The earliest known Buddhist writings of Sri Lanka, known collectively as the Pāli canon, date to the fourth Buddhist council, which took place in 29 BCE. Sri Lanka's geographic location and deep harbours have made it of great strategic importance, from the earliest days of the ancient Silk Road trade route to today's so-called maritime Silk Road. Because its location made it a major trading hub, it was already known to both Far Easterners and Europeans as long ago as the Anuradhapura period. The country's trade in luxury goods and spices attracted traders of many nations, which helped to create Sri Lanka's diverse population. During a period of great political crisis in the Sinhalese kingdom of Kotte, the Portuguese arrived in Sri Lanka (largely by accident) and then sought to control the island's maritime regions and its lucrative external trade. Part of Sri Lanka became a Portuguese possession. After the Sinhalese-Portuguese war, the Dutch and the Kingdom of Kandy took control of those areas. The Dutch possessions were then taken by the British, who later extended their control over the whole island, colonising it from 1815 to 1948. A national movement for political independence arose in the early 20th century, and in 1948, Ceylon became a dominion. The dominion was succeeded by the republic named Sri Lanka in 1972. Sri Lanka's more recent history was marred by a 26-year civil war, which began in 1983 and ended decisively in 2009, when the Sri Lanka Armed Forces defeated the Liberation Tigers of Tamil Eelam.Today, Sri Lanka is a multinational state, home to diverse cultures, languages, and ethnicities. The Sinhalese are the majority of the nation's population. The Tamils, who are a large minority group, have also played an influential role in the island's history. Other long established groups include the Moors, the Burghers, the Malays, the Chinese, and the indigenous Vedda.The island has had a long history of engagement with modern international groups: it is a founding member of the SAARC and a member of the United Nations, the Commonwealth of Nations, the G77, and the Non-Aligned Movement. Sri Lanka is the highest-ranked South Asian nation on the Human Development Index and has the second-highest per capita income in South Asia.