This essay examines the impact of Roberto Matta’s presence in the United States during 1939–1948, when, as part of a Surrealist cohort of émigrés, he established temporary residence in New York to escape the war in Europe. The authors characterize Matta’s presence in New York as “catalytic” at a precise historical moment of a cultural shift in which the group of artists that would form the core of Abstract Expressionism and the New York School were in the process of redefining American art. Matta became the transmitter of Surrealist ideas and techniques, helping artists liberate their art from a dominant Cubist grid by introducing them to automatism, a new style and approach to abstraction, and to iconography that fused psychic and physical inner and outer universes, symbolisms, and myths. The authors provide an extensive analysis of Matta’s work during this New York period, as well as a detailed historical account of his relationships with dealers, artists, and intellectuals in New York. In their analysis of his development, they classify his work into two general periods of about four years each, the first of which was characterized by his concern with the inner self and the world around him reflected in his psychological morphology paintings. The second period was characterized by his preoccupation, beginning in 1943, with the war in Europe, social despair and fragility of human existence, and man’s place in the world reflected in his social morphology paintings, which unlike work from the previous period, featured the human figure.