The Social Democratic Party of Finland (SDP, Finnish: Suomen sosialidemokraattinen puolue [ˈsuo̯men ˈsosiɑ(ː)liˌdemokrɑːtːinen ˈpuo̯lue]; Swedish: Finlands socialdemokratiska parti), shortened to the Social Democrats (Finnish: Sosiaalidemokraatit; Swedish: Socialdemokrater) and commonly known in Finnish as Demarit (Swedish: Socialdemokraterna), is a social-democratic political party in Finland. It is currently the largest party in the Parliament of Finland with 40 seats.

Founded in 1899 as the Finnish Labour Party (Finnish: Suomen työväenpuolue; Swedish: Finska arbetarpartiet), the SDP is Finland's oldest active political party and has a close relationship with the Central Organisation of Finnish Trade Unions. It is also a member of the Party of European Socialists, Progressive Alliance, Socialist International and SAMAK.

Following the resignation of Antti Rinne in December 2019, Sanna Marin became the country's 67th Prime Minister. SDP formed a new coalition government on the basis of its predecessor, in effect continuing cooperation with the Centre Party, the Green League, the Left Alliance and the Swedish People's Party. Seven of the government's nineteen ministers are SDP members.