What is the most important form of classical chamber music?

The most important form of classical chamber music is the string quartet. A string quartet is a musical ensemble of four string instruments, typically two violins, a viola, and a cello. The string quartet is considered one of the most prestigious and challenging genres of chamber music, as it requires a high level of technical skill and musicianship from all four players. String quartets have been composed by some of the most famous composers of classical music, including Haydn, Mozart, Beethoven, and Brahms.