Lady Be Good is a really nice standard tune by George and Ira Gershwin. They wrote the tune for a 1924 musical “Lady Be Good.” Incidentally, Fascinating Rhythm was another jazz standard that was written for the same musical by the Gershwin brothers. Ella Fitzgerald, Benny Goodman, and Ray Brown all made Lady Be Good one of their signature tunes, and many other artists have recorded it as well.
This tune is mostly commonly performed in the key of G, although sometimes it’s performed in F or even in C.