Leonard Gilbert Ratner (July 30, 1916 – September 2, 2011) was an American musicologist and Professor of Musicology at Stanford University.
He was a specialist in the style of the Classical period and is best known as a developer of the concept of topic theory (see music semiology).
He studied the violin and viola, as well as composition with Frederick Jacobi, Arnold Schoenberg, Ernest Bloch, and Arthur Bliss.
He taught composition and theory to advanced students and coached chamber music; he also taught elementary music appreciation courses for undergraduates, Stanford alumni, and the general public.
He was awarded a Guggenheim Fellowship (1962) and elected as a Fellow of the American Academy of Arts and Sciences in 1998.