The piano is the best loved of musical instruments, thanks in part to the elegant symmetrical design of its ivory and ebony keyboard that ensures each pitch is reliably equidistant from the next. But this 'equal temperament' tuning was once a hugely controversial notion. It is difficult now to imagine the keyboard as other than it is; yet this was precisely what many European musicians practising before the nineteenth century demanded of their instruments. For hundreds of years, musicians, craftsmen, church officials, heads of state and philosophers fought heatedly against the introduction of 'equal temperament' tuning. Stuart Isacoff hereby recounts this great battle over the best way to create music - a battle that culminated in the destruction of the harpsichord and the emergence, from its flames, of the piano. Why the resistance to equal temperament lasted so long, and how it was finally overcome, is a story that encompasses crucial elements of Western culture - social history, religion, philosophy, science, economic development - in a period when Europe was struggling to give birth to the modern age.