The Socialist Party is a social-democratic political party in Portugal. It was founded on 19 April 1973 in the German city of Bad Münstereifel by militants who were at the time with the Portuguese Socialist Action. The PS is a member of the Socialist International, Progressive Alliance and Party of European Socialists, and has nine members in the European Parliament within the Progressive Alliance of Socialists and Democrats group during the 9th European Parliament. It was the governing party of Portugal between November 2015 and April 2024, subsequently winning the 2019 and 2022 legislative elections.

The Socialist International (SI) is a political international or worldwide organisation of political parties which seek to establish democratic socialism, consisting mostly of social-democratic political parties and labour organisations.