The United Socialist Party (Romanian: Partidul Socialist Unitar, abbreviated P.S.U.) was a political party in Romania, formed in 1933 through the merger of the Independent Socialist Party (PSI) and the Socialist Party (led by Constantin Popovici). PSU was a small party but played an important role within the left-wing movement, especially through its repeated attempts to promote unity between the Communist Party (PCR) and (PSD). PSU was affiliated with the London-based International Bureau of Revolutionary Socialist Unity.