Ronald Martin Foster (3 October 1896 – 2 February 1998), was an American mathematician at Bell Labs whose work was of significance regarding electronic filters for use on telephone lines. He published an important paper, A Reactance Theorem,^[1] (see Foster's reactance theorem) which quickly inspired Wilhelm Cauer to begin his program of network synthesis filters which put the design of filters on a firm mathematical footing.^[2] He is also known for the Foster census of cubic, symmetric graphs^[3] and the 90-vertex cubic symmetric Foster graph.

Foster was a Harvard College graduate S.B. (Mathematics), summa cum laude, Class of 1917. He also received two honorary Sc.D.s.^[3]

• 1917 – 1943 Research & Development Department (later Bell Labs), American Telephone & Telegraph, as a Research Engineer (Applied Mathematician), New York City, New York.
• 1943 – 1963 Professor and Head of Department of Mathematics, Polytechnic Institute of Brooklyn, Brooklyn, New York City, New York.

• Campbell, GA, Foster, RM, Fourier Integrals for Practical Applications, "Bell System Technical Journal", pp 639–707, 1928.^[4]
• Pierce, BO, Foster. RM. "A Short Table of Integrals", Fourth Edition, Ginn and Company, pp 1–189, 1956.