The Social Christian Unity Party (Spanish: Partido Unidad Social Cristiana) is a centre-right political party in Costa Rica.^[1]

PUSC considers itself a Christian-democratic party and, as such, is a member of the Christian Democrat Organization of America (ODCA). It was founded in 1983 by merger of the parties that were part of the Unity Coalition: the Christian Democratic, the Republican Calderonista, People's Union and the Democratic Renovation Party. Its historical roots are in Calderonism, i.e. the movement of supporters of Rafael Ángel Calderón Guardia, who was the country's president in the 1940s. From its foundation until 2006, the PUSC was one of Costa Rica's two dominant parties, alongside the National Liberation Party. It provided three presidents: Rafael Ángel Calderón Fournier (1990–94), Miguel Ángel Rodríguez (1998–2002) and Abel Pacheco (2002–06).

Negotiations among the main right-wing opposition parties to create a political force capable of confronting the National Libertation Party (PLN) started as early as 1973. Yet, wasn’t until 1977 that four political parties; People's Union (liberal), Christian Democratic Party (Christian Democracy), Republican Calderonista (Calderonism) and Democratic Renovation (Social democracy) united forces in the Unity Coalition. After a primary election Rodrigo Carazo became the alliance's nominee gaining victory in the 1978 general election.^[2] The Coalition not only achieved the Presidency but also a non-PLN parliamentary majority for the first time since PLN's foundation. Yet, Carazo's administration was very unpopular due to the economic crisis and the tensions with neighbor Nicaragua due to Costa Rica's support of the rebel guerrilla FSLN. Thus, Rafael Ángel Calderón Fournier the Coalition's candidate in the 1982 general election suffered a debacle gaining only 33% of the votes and PLN obtaining a landslide victory. Even though, Unity remained as the second political force.^[2]

On December 17, 1983, the four parties merged in the Social Christian Unity Party, not without certain controversy especially among certain factions in the Democratic Renovation. Costa Rica's law required for every party in the coalition to merge in order to be valid and also to be able of receiving the so call “political debt” (State's contribution to parties after the election proportional to their electoral support). After a series of complex sessions, Democratic Renovation's National Assembly finally agree by a slight majority to merge and PUSC was born and Costa Rica passed from a dominant-party system into a two-party system with PLN and PUSC as main political forces.

PUSC’ first primary was held on February 27, 1989. Calderón Fournier faces Miguel Ángel Rodríguez Calderón winning with 75% of the votes. Calderón, as the son of Rafael Ángel Calderón Guardia, the historical leader of Calderonism and the social reforms of the 40s,^[2] was seen as the most representative leader of PUSC, while Rodríguez came from the liberal faction inside the party. This division between liberals and calderonistas was going to survive for the rest of the Party's history.^[2]

In the 1990 election following that primary Calderón won over PLN's candidate Carlos Manuel Castillo.^[3] A second primary was held on June 1993 between Rodríguez and Juan José Trejos (son of former president José Joaquín Trejos), this time Rodríguez turned victorious with 75% but lost to PLN's candidate José María Figueres in 1994.^[2] With Rodríguez as candidate the party did won both Presidency and parliamentary majority in the 1998 election, this time without the need for primaries.^[2]

Next primary was held on June 10, 2001 between then deputy and TV personality Dr. Abel Pacheco de la Espriella and former minister Rodolfo Mendez Mata. Even though Mata was endorsed by Calderón, Pacheco won the primary with 76% of the votes. Pacheco won the 2002 election over PLN's candidate Rolando Araya making it the first time a party other than PLN kept in power by two consecutive terms since 1948.^[2]