The centre-left coalition (Italian: coalizione di centro-sinistra) is a political alliance of political parties in Italy active under several forms and names since 1995, when The Olive Tree was formed under the leadership of Romano Prodi. The centre-left coalition has ruled the country for more than thirteen years between 1996 and 2021; to do so, it had mostly to rely on a big tent that went from the more radical left-wing, which had more weight between 1996 and 2008, to the political centre, which had more weight during the 2010s, and its main parties were also part of grand coalitions and national unity governments.

The coalition mostly competed with the centre-right coalition founded by Silvio Berlusconi. In the 1996 Italian general election, The Olive Tree consisted of the majority of both the left-wing Alliance of Progressives and the centrist Pact for Italy, the two losing coalitions in the 1994 Italian general election, the first under a system based primarily on first-past-the-post voting. In 2005, The Union was founded as a wider coalition to contest the 2006 Italian general election, which later collapsed due to Clemente Mastella during the 2008 Italian political crisis, with the fall of the second Prodi government.

In the late 2000s and early 2010s, the centre-left coalition has been built around the Democratic Party (PD), which was established in 2007 from a merger of Democrats of the Left and Democracy is Freedom, the main parties affiliated to both The Olive Tree and The Union. The centre-left coalition was part of Italian governments from November 2011 to June 2018, when a coalition government between the Five Star Movement (M5S) and the League was formed.

In September 2019, the centre-left returned to power in coalition with the M5S, with centre-left parties participating in the national unity government of Mario Draghi, who was the country's prime minister from February 2021 until the 2022 Italian government crisis in July that led to the 2022 Italian general election. Under an electoral law (Rosatellum) that favoured unity and coalitions, a divided centre-left, M5S, and PD's centrist split parties suffered a loss to the centre-right coalition, which won a majority of seats since the 2008 Italian general election. Since 2023, PD, M5S, Greens and Left Alliance (AVS) and minor centre-left parties often run within the same coalition at local and regional level in the Progressive Camp.

Following the 1994 Italian general election, which was won by the centre-right coalition of Silvio Berlusconi, the left-wing Alliance of Progressives and the centrist Pact for Italy started a parliamentary cooperation, which brought in March 1995 to the foundation of The Olive Tree. The historical leader and ideologue of these coalitions was Romano Prodi, Professor of Economics and former member of Christian Democracy (DC), who invented the name and the symbol of The Olive Tree with Arturo Parisi in 1995.

In 1995, Lega Nord exited the Pole of Freedoms and supported Lamberto Dini's technocratic government, together with the Pact for Italy and the Alliance of Progressives. On 21 April 1996, The Olive Tree won 1996 Italian general election with the Communist Refoundation Party (PRC) as an external ally, making Romano Prodi the Prime Minister of Italy. The Olive Tree's largest partner was the Democratic Party of the Left (PDS), which contained the bulk of the former Italian Communist Party. The PDS supplied 16 ministers and 10 junior ministers; it was the first time that former PCI members had taken part in government since 1947. One of their leaders, Walter Veltroni, who ran in ticket with Prodi in a long electoral campaign, was Deputy Prime Minister of Italy. On 9 October 1998, the first Prodi government fell when PRC left the alliance. Since 21 October 1998, The Olive Tree was the core of the governments led by Massimo D'Alema and by Giuliano Amato. When D'Alema became the new prime minister, it was the first time ever in both Italy and Western Europe that an heir of the Communist party tradition came to lead a government. On 13 May 2001, led by Francesco Rutelli, who ran in ticket with Piero Fassino, the centre-left coalition lost the general elections against Berlusconi and the House of Freedoms.

The Union was the direct heir of The Olive Tree. While The Union was an heterogenous alliance that also included Communist parties, they were not part of The Olive Tree. Prodi won the 2006 Italian general election by a very narrow margin due to the new electoral law enacted by Roberto Calderoli; Berlusconi refused to acknowledge defeat. Prodi's coalition proved to be extremely frail, as the two-vote margin in the Senate of the Republic allowed almost any party in the coalition to veto legislation and political views inside the coalition spanned from communists to Christian democrats.

On 7 May 2006, the centre-left coalition officially endorsed Giorgio Napolitano as its candidate in the 2006 Italian presidential election that began on 8 May. The Holy See endorsed him as the president of Italy through its official newspaper, L'Osservatore Romano, just after The Union named him as its candidate, as did Marco Follini, former secretary of the Union of Christian and Centre Democrats (UDCC), a member party of the House of Freedoms. On 10 May 2006, Napolitano was elected in the fourth round of voting, the first of those requiring only an absolute majority, unlike the first three which required two-thirds of the votes, with 543 votes (out of a possible 1009). At the age of 80, he became the first former PCI member to become president of Italy