The most expensive musical instrument ever sold is the "Lady Blunt" Stradivarius violin, which was auctioned in 2011 for approximately $15.9 million. Made in 1721 by the renowned luthier Antonio Stradivari, the "Lady Blunt" is one of the best-preserved Stradivarius violins in existence. The high price is attributed to its rarity, historical significance, and the craftsmanship of Stradivari, whose instruments are considered some of the finest ever made.