Although now commonly adopted as the point of reference for musicians in the Western world, “A” 440hz only became the standard pitch during an international conference held in London in 1939. The adoption of this norm was the result of decades of international negotiations launched in Stuttgart in 1834, involving a surprisingly dynamic mix of actors. If performers first raised the cry for musical standardization, composers were quick to follow in order to assert their authority in the field of aesthetics. At the same time, instrument builders’ participation in the negotiations revealed the stakes that standardization held for the sale of their products internationally, while physicists’ motivations were engendered by a scientific faith in being able to rationally determine the most accurate pitch for performance. Finally, representatives of different state ministries showed themselves eager to impose their nation’s norms as a sign of their cultural and scientific superiority. Which actors and countries were empowered in the negotiations? What were the procedures that finally led to the decision made by the 1939 London conference? By answering such questions, this work will demonstrate the political, technological, scientific, and aesthetic contingencies underlying the historical construction of one of the most “natural” and seemingly stable objects of contemporary musical performance, itself the result of a cacophony of competing views and interests, and chart the changing maps of forces in charge of literally tuning the world.