Jesu, Joy of Man's Desiring is one of the most widely-recognized and widely-performed works of classical music. But the famous chorale melody so familiar at formal occasions was written not by Johann Sebastian Bach.
As was common during Bach's time, this cantata made use of a previously existing chorale melody by Johann Schop written 74 years earlier.
The cantata in which we find Bach's version of the melody is the 32nd of his surviving cantatas, but it's label 147th in the BWV classification system.
The letters BWV are the German abbreviation for "Bach Works Catalog," a system created in 1950 by Wolfgang Schmieder to order the many works of Bach. Many other composers have unique systems such at Mozart's Koechel and Schubert's Deutch, but the Schmieder's is one of the only that doesn't bear the name of it's creator.