Quartets—ensembles of four instruments or voices—have been around for as long as music itself. Today, however, the word ‘quartet’ usually refers to the string variety (two violins, viola and cello), invented by Joseph Haydn in the mid 18th century and championed from then on by most of the great composers. You’ll find some of those great works here, but we’ve also delved a little deeper to showcase what composers can do with a quartet of any instruments. May the four be with you.