String Quartet No. 1 in C major, Op. 37, is a composition for string quartet by Karol Szymanowski. It was the first of the two string quartets composed by Szymanowski. The work is from 1917 during his middle period. It is notable for its "polytonal" third movement, which contains four key signatures in its written four parts: the first violin with 3 sharps, the second violin with 6 sharps, the viola with 3 flats, and the cello with no flats or sharps.