Ronald Martin Foster (3 October 1896 – 2 February 1998), was a Bell Labs mathematician whose work was of significance regarding electronic filters for use on telephone lines.
He published an important paper, A Reactance Theorem, (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.
He is also known for the Foster census of cubic symmetric graphs and the 90-vertex cubic symmetric Foster graph.