UDSR , abbreviation of democratic and socialist Union of Resistance. Formation resulting from the Resistance, it set up a hinge group under IVe République. Principal personalities: François Mitterrand and Rene Pleven. It was associated with the radicals within the Rassemblement of the Republican lefts.

Exit of Resistance (as its name indicates it) and more precisely of the Liberation movement Main road (MLN), the UDSR ambitionnait to become the great Labor force of government. It was to be initially called besides Labor Union of Release . Mow, the reconstitution of SFIO buries its hopes, and the UDSR must be satisfied to play an auxiliary part at the Parliament.

It amalgamates since 1946 with the Democratic party , political party founded with the Release by old the resistant resulting ones from the popular Democratic party refusing the transformation of the PDP into MRP.

Sometimes classified in the center, even with the center-right in spite of its name, the UDSR is regarded by the recent historical research as an authentic attempt at a liberal socialism not Marxist. Besides it forms part of the organizations founders of the liberal Internationale.

The UDSR is a party hinge of the 4th Republic. He plays a very important part, in particular in the liberal inflection of the colonial policy as from 1950. Rene Pleven (president of the Council) and François Mitterrand (Minister of France of overseas) obtains the political alliance of the African democratic Gathering with the UDSR and improves the fate of the populations of Black Africa. According to Eric Duhamel, they thus save these colonies of the violence which would have caused the maintenance of a policy of oppression and preserving.

The election of François Mitterrand to the presidency of the party, in 1953, mark a centring on the left.

The UDSR perdure until 1965, finally being based in the Center of Institutional Action , become then the Convention of the Republican Institutions, François Mitterrand. She had been gradually deserted by all her organizers non-mitterrandists, parties to join formations gaullists, gaullists of left or Christian-Democrat.