What is what key is french horn in?

The French horn is a transposing instrument, which means that the pitch it plays sounds different from the written pitch. The French horn is usually pitched in F, meaning that when a horn player reads a C in the sheet music, they will produce an F sound. This is because the French horn is a horn in the key of F. However, there are also double horns that have an extra set of tubing and can switch between keys of F and Bb. This allows horn players to play in different keys without having to transpose manually.