Bach's toccatas are among the most famous examples of the form, and his Toccata and Fugue in D minor, BWV 565 is one of the most popular organ works today, although its authorship is disputed by some authorities. His toccatas for organ are improvisatory compositions, and are often followed by an independent fugue movement. In such cases, the toccata is used in place of the usually more stable prelude. Bach's toccatas for harpsichord are multi-sectional works which include fugal writing as part of their structure.