Transposing instruments are musical instruments that sound different from the written notes. For example, when a B♭ trumpet plays a written C, it actually sounds a B♭. This means that musicians must adjust the written music to match the instrument's pitch, which can be challenging for composers and performers. Common transposing instruments include the clarinet, saxophone, and French horn. Each of these instruments has its own transposition rules, often based on their key. Understanding transposition is essential for musicians to ensure that all players are in tune and can perform together harmoniously.