The Italian Republican Party is a political party in Italy established in 1895, which makes it the oldest political party still active in the country. The PRI identifies with 19th-century classical radicalism, as well as Mazzinianism, and its modern incarnation is associated with liberalism, social liberalism, and centrism. The PRI has old roots and a long history that began with a left-wing position, being the heir of the Historical Far Left and claiming descent from the political thought of Giuseppe Mazzini and Giuseppe Garibaldi. With the rise of the Italian Communist Party and the Italian Socialist Party (PSI) to its left, it was associated with centre-left politics. The early PRI was also known for its anti-clerical, anti-monarchist, republican, and later anti-fascist stances. While maintaining those traits, during the second half of the 20th century the party moved towards the centre on the left–right political spectrum, becoming increasingly economically liberal.

Radicalism was a political movement representing the leftward flank of liberalism during the late 18th and early 19th centuries and a precursor to social liberalism, social democracy, civil libertarianism, and modern progressivism. This ideology is commonly referred to as "radicalism" but is sometimes referred to as radical liberalism, or classical radicalism, to distinguish it from radical politics. Its earliest beginnings are to be found during the English Civil War with the Levellers and later the Radical Whigs.