  A systematic expansion in 1/N is constructed for baryons in QCD. Predictions
of the 1/N expansion at leading and subleading order for baryon axial current
coupling constant ratios such as F/D, baryon masses and magnetic moments are
derived. The baryon sector of QCD has a light quark spin-flavor symmetry at
leading order in 1/N. The formalism of induced representations for contracted
Lie algebras is introduced to explain the consequences of this symmetry.
Relations are first derived for the simplest case of two light flavors of
quarks. The generalization of the large N expansion to N_f = 3 flavors is
subtle and is treated using several complementary methods. The 1/N expansion
severely restricts the form of SU(3) breaking in the baryon sector.
Extrapolation of the large N results to N=3 permits quantitative comparison
with experimental data. Deviations of the measured quantities from exact
spin-flavor symmetry predictions are accurately described by the subleading 1/N
corrections. Implications of the 1/N expansion for baryon chiral perturbation
theory are discussed.
