The Radical Party (Italian: Partito Radicale, PR) was a liberal and left-libertarian political party in Italy. For decades, inspired by 19th-century radicalism, the Radical Party was a bastion of anti-clericalism, civil libertarianism, feminism, liberalism and radicalism in Italy as well as environmentalism. The party proposed itself as the strongest opposition to the Italian political establishment, seen as corrupt and conservative. Although it never reached high shares of vote and never participated in government, the party had close relations with the other parties of the Italian left—from the Republicans and the Socialists to the Communists and Proletarian Democracy—and opened its ranks also to members of other parties through dual membership.

The party's longtime leader was Marco Pannella (1930–2016), who served as a member of the Chamber of Deputies (1976–1994) and the European Parliament (1979–2009), leading the party in most of the elections it contested. In 1989, the PR was transformed into the Transnational Radical Party, a non-governmental organisation tasked with defending liberal and left-libertarian values. During the 1990s, the Radicals had formed a succession of electoral lists (notably including the Pannella List and Bonino List), without having a structured party and sometimes dividing themselves between competing lists. The latest incarnation of the party is the Italian Radicals, founded in 2001, former section of Transnational Radical Party.

The PR was founded in 1955 by the left wing of the Italian Liberal Party as the ideal continuation of the historical Radical Party, active from 1877 to 1925, emphasising liberal and secular issues such as separation of church and state and the full implementation of the Constitution. Leading members of the new party included Bruno Villabruna, Mario Pannunzio, Ernesto Rossi, Leo Valiani, Guido Calogero, Giovanni Ferrara, Paolo Ungari, Eugenio Scalfari and Marco Pannella.

Following a leadership crisis in 1963, most party members left the PR and joined the Italian Socialist Party or the Italian Republican Party; the remaining members, under the leadership of Pannella and Gianfranco Spadaccia took control of the party, which abandoned its original social-liberal views and adopted a strong left-libertarian position. The "new" PR came to political success in the 1976 general election, when it entered Parliament with four deputies: Pannella, Emma Bonino, Adele Faccio and Mauro Mellini. In the 1979 general election, the party won 3.5% of the vote and elected 18 deputies and two senators, its best result ever and by far the largest gain of any party in the Chamber of Deputies.

The relative success of the party was a consequence of the new line impressed by Pannella who moved the party's focus to issues like divorce and abortion, also by winning three referendums on those issues in 1974 and 1981. In 1979, following the first European Parliament direct election, the PR was involved with Coordination of European Green and Radical Parties (CEGRP) and its unsuccessful efforts to create a single pan-European platform for green and radical politics.

From 1976, the PR used the fist and rose emblem created by the French Socialist Party and later used by the Socialist International, although they were not ideologically close: Pannella had managed to obtain the permission because the Italian Socialist Party (PSI) lacked internal support to remove its traditional symbols, which included the Marxist hammer and sickle. In 1980, it decided to add a thick, diagonal black armband as a sign of mourning to its logo to pay homage to the part of humanity which was victim of hunger and war, reflecting its internationalist turn.

In the 1980s, the party focused more on international and European issues. Affiliated to the Coordination of European Green and Radical Parties/European Green Coordination, Pannella was a member of the European Parliament since 1979 and led the party into new battles against hunger and in favour of further European integration. The party European affiliation were the Technical Group of Independents (1979–1984), Non-Inscrits (1984–1989) and Green Group. In 1989, the party was transformed into the Transnational Radical Party, a non-governmental organisation working at the United Nations and coordinating the efforts of several national parties and groupings mainly in support of human rights. The Radicals continued to participate in elections through the Antiprohibitionists on Drugs list, the Rainbow Greens, the Pannella List, the Bonino List and the Bonino-Pannella List. In 2001 they re-organised themselves as a party with the Italian Radicals and Bonino served in two governments (Prodi II – 2006–2008 and Letta – 2013–2014). Pannella died after a long illness in 2016.

The PR gave expression to the transformation of Italian society towards more liberal behaviour and ideas in the post-war period. An anti-clerical party, it placed itself within the libertarian left, often working for the unity of all the parties of the Italian left and proposing the adoption of an American-style electoral system based on first-past-the-post voting and the transformation of Italian institutions toward a presidential system, but also often being rejected by certain areas of the left itself, especially those linked with the Italian Communist Party, due to the Radicals' strong support of anti-communism, their economic liberalism, and their belief in social, religious, political, economic, and sexual freedoms. The party was also known for its strong belief in direct democracy and especially for its promotion of referendums.