Rudolph Maurice Loewenstein (January 17, 1898, in Łódź, Congress Poland, Russian Empire - April 14, 1976, in New York City) was a Polish-French-American psychoanalyst.
After studying medicine and neurology in Zurich, Loewenstein was analyzed in Berlin by Hans Sachs. He became a member of the German Psychoanalytic Society (DPG) in 1925. The same year he began to practice as a teaching analyst in Paris, where he trained a number of future analysts, including, notably, Jacques Lacan (between 1933 and 1939). In 1926, he founded the first French psychoanalytic society, the Société psychanalytique de Paris (SPP), along with eight other psychoanalysts, including René Laforgue, Marie Bonaparte, Raymond de Saussure, and Angelo Hesnard. He was elected secretary of the SPP. In 1927, he participated in the creation of the Revue française de psychanalyse.
In 1930, he became a French citizen and began his studies anew - defending his thesis for a doctorate in medicine in 1935. In 1939, he was mobilized as a doctor in the French army. After the Armistice, he fled to the south of France and from there left for the United States, where he settled in New York. There he pursued a distinguished institutional career with the International Psychoanalytic Association (IPA), becoming its vice president from 1965 to 1967.
Loewenstein is known, along with Ernst Kris and Heinz Hartmann, as one of the foremost figures of what has been called Ego psychology.