In these lectures we review the motivation, principles of and
(circumstantial) evidence for the program of unification of the fundamental
forces. In an appendix, we review the group theory pertinent to the program.Comment: 28 pages plain LaTeX, to be run twice. Lectures given at the Sixth
ICTP-BCSPIN School on Current Trends in High Energy Physics and Cosmology,
Kathmandu, Nepal, May 19-June 3 199