Robert Smith (1689 - February 2, 1768) was an English mathematician.

Smith was probably born at Lea near Gainsborough. After attending Leicester Grammar School he entered Trinity College, Cambridge, in 1708, and becoming minor fellow in 1714, major fellow in 1715 and senior fellow in 1739, was chosen Master in 1742, in succession to Richard Bentley. From 1716 to 1760 he was Plumian Professor of Astronomy, and he died in the Master's Lodge at Trinity.

Besides editing two works by his cousin, Roger Cotes, who was his predecessor in the Plumian chair, he published A Compleat System of Opticks in 1738, which gained him the sobriquet of Old Focus, and Harmonics, or the Philosophy of Musical Sounds in 1749. He was the founder of the Smith's Prizes at Cambridge, having by his will left £3500 South Sea stock to the University, a portion of the interest from which was to be divided yearly between the two junior BA.s who had made the greatest progress in mathematics and natural philosophy.