The Democratic and Socialist Union of the Resistance (Union démocratique et socialiste de la Résistance or UDSR) was a French centerist political party.

It was founded in 1945 by the non-Communist resistant network Movement of National Liberation. The project was to create a French labour party with all the former non-Communist Resistance. However, that was not possible because of the rebirth of the socialist party SFIO, and the emergences of the christian democratic party MRP and the gaullist party RPF. Sfio, or Safe/Fast I/O, is an I/O library developed by AT&T Research, with several improvements over the ANSI C stdio library. ... The Popular Republican Movement (Mouvement Républicain Populaire or MRP) was a French Christian democratic party of the Fourth Republic. ... In France the Gaullist Party is usually used to refer to the largest party professing to be Gaullist. ...

Associated with the Radical Party in the Rally of the Republican Lefts (Rassemblement des gauches républicaines or RGR), the UDSR was during the Fourth Republic a minor centerist political party which participated to the governments. In this, its president René Pleven was Prime Minister from 1951 to 1952. But, his leadership over the party was challanged by François Mitterrand who advocated a realignment to the Left. He took the lead in 1953. To meet Wikipedias quality standards, this article or section may require cleanup. ... There were several Fourth Republics in the course of history. ... René Pleven, French prime minister René Pleven (April 1901 - January 13, 1993) was a notable French politician of the Fourth Republic. ... (October 26, 1916 – January 8, 1996) was a French politician. ...

In 1956, the UDSR participated to the center-left coalition "Republican Front", which won the legislative election. However, two years later, the party imploded. Indeed, Pleven and the conservative wing approved Charles de Gaulle's come back and the Fifth Republic, contrary to Mitterrand. Charles André Joseph Marie de Gaulle ( ) (22 November 1890 – 9 November 1970), in France commonly referred to as Général de Gaulle, was a French military leader and statesman. ... The Fifth Republic is the fifth and current republican constitution of France, which was introduced on October 5, 1958. ...