Marcel Grossmann (April 9th 1878 with Budapest, Hungary - September 7th 1936 with Zurich, Swiss) is a Mathématicien Hungarian. He is especially known to have helped Albert Einstein to build the theory of the General relativity.

After having supplemented its doctorate in descriptive Geometry at the polytechnic Institute of Zurich (ETH), become today ETHZ, it becomes Professor there mathematics.

Colleague of class to the ETH and friend of Albert Einstein, Grossmann directed in an unquestionable way Einstein towards the not-Euclidean geometries, necessary to the construction of the theory of the General relativity. He gave to this last the tools to control the Tenseur S, mathematical objects essential with the formulation of this theory.

They wrote together one of the first, if not the first, article on general relativity: Albert Einstein and Marcel Grossmann, Entwurf einer verallgemeinerten Relativitätstheorie und einer Theory DER Gravitation , Zeitschrift für Mathematik und Physik, 62:225, 1914. During the drafting of the article, Grossmann dealt with the mathematical part, whereas Einstein dealt with the physical part.