The 35.56 ct Wittelsbach Blue is one of the largest historic blue diamonds ever fashioned. It belonged to the Bavarian House of Wittelsbach and was displayed in the Treasury of the Munich Residence until it disappeared in 1931. It was secretly sold in 1951, “rediscovered” in 1961, and then sold again in 1964 to an undisclosed private buyer. In December 2008, the Wittelsbach Blue was sold at Christie’s London to jeweler Lawrence Graff for just over $24.3 million, a record price for any diamond at auction. This article describes what is known about the Wittelsbach Blue since it was first reported in 1666, and the gemological information released to date on this diamond, which was recently graded Fancy Deep grayish blue. Investigations in the historical archives of Bavaria, Austria, and Spain revealed that there is no archival evidence to support many previous statements about this stone.