Italian Left (Italian: Sinistra Italiana, SI) is a left-wing political party in Italy. SI was launched in November 2015 as a parliamentary group in the Chamber of Deputies (full name: Italian Left – Left Ecology Freedom), including Left Ecology Freedom (SEL), dissidents from the Democratic Party like Future to the Left, and splinters from the Five Star Movement. At its launch, SI included 32 deputies, who were soon followed by eight senators (who formed a sub-group within the Mixed Group of the Senate in February 2016), and two MEPs. SI was officially formed as a full-fledged party in February 2017, after SEL had chosen to merge into it in December 2016.

The party is led by Nicola Fratoianni. Notable founding members included Nichi Vendola (former leader of SEL), Loredana De Petris, Stefano Fassina, and Sergio Cofferati. In the aftermath of its founding congress, 18 deputies left the party, leaving it with 13 deputies, eight senators and 2 MEPs: 17 deputies, led by former group leader Arturo Scotto, joined the brand-new Article One, while Laura Boldrini (President of the Chamber of Deputies) joined the Chamber's Mixed Group. In late 2017, the party was a founding member of Free and Equal, a left-wing joint list for the 2018 general election, and more recently in 2022 founded the Greens and Left Alliance (AVS) with Green Europe.

In June 2015, Stefano Fassina, a former deputy minister in the Letta Cabinet, left the Democratic Party (PD) over disagreements with Matteo Renzi, then PD leader and Prime Minister. In doing this he was followed by his long-time ally Monica Gregori [it]. In July, during a convention, Fassina launched Future to the Left (FaS), an incubator of a new left-leaning party, with other movements and breakaway groups such as Possible (Pos) and Left Ecology Freedom (SEL).

In November, one senator (Corradino Mineo) and three more deputies (Alfredo D'Attorre [it], Carlo Galli [es; it] and Vincenzo Folino [it]) left the party in protest against Renzi. D'Attorre, who holds a doctorate in philosophy from the Sant'Anna School of Advanced Studies, wrote a manifesto for a new "labour" party, which was signed also by the other five MPs and, which read: "The genetic mutation of the PD, born as central force of the Italian centre-left, is unfortunately already completed. The Renzi experience and the introduced mutations won't be a parenthesis. They have already altered in an irreversible way the perception of the PD and its function in the collective imagination". Subsequently, a parliamentary group under the banner of Italian Left was formed in the Chamber of Deputies, whose core was formed by SEL.

In February 2016, SI held its constituent assembly in Rome. Consequently, SI was established as a sub-group within the Mixed Group in the Senate: five senators of SEL, two dissidents from the Five Star Movement (Fabrizio Bocchino [it] and Francesco Campanella [it]) and one former Democrat (Mineo) joined, while two SEL senators (including Sardinian nationalist Luciano Uras [fr; it]) refused to join and left their party altogether.

Several lists named after SI participated in the 2016 local elections. The party did particularly well in Sesto Fiorentino, a medium-sized city in the metropolitan area of Florence, where it won 17.5% of the vote and its candidate for mayor was elected in the run-off with 65.5%, by beating his Democratic opponent.

In December 2016, SEL was dissolved, to merge it into SI in early 2017.

In February 2017, SI was officially formed and Nicola Fratoianni was elected as its first secretary.