Joseph Haydn's string quartets, sometimes catalogued as Op. 64 are a set of six string quartets composed in 1790. Along with six earlier quartets published under the opus numbers 54 and 55, they are known as the Tost quartets, after the Hungarian violinist and later merchant Johann Tost who helped Haydn find a publisher for the works. Unlike the earlier quartets, Haydn actually dedicated the Op. 64 set to Tost in gratitude for his efforts.
