The large Nc limit plays a fundamental role in the study of non-abelian gauge theories such as quantum chromodynamics (QCD). Since its discovery in 1974 by 't Hooft, the 1/Nc expansion has provided crucial insights into the non-perturbative aspects of gauge theories. The expansion implemented at the effective theory level is one of the fundamental tools currently in use in hadronic physics; there are important effects and relations that follow from the 1/Nc expansion, which held remarkably well in the real world with Nc= 3. The 1/Ncexpansion also plays a central role in the recently discovered connections between non-Abelian gauge and string theories, promising new ways to analyze the non-perturbative domain of gauge theories.This volume contains contributions from leading theorists and covers the recent developments in the 1/Nc expansion in QCD. The topics addressed include confinement, AdS/CFT correspondence and the string-QCD connection, topology in large Nc, lattice QCD, and a variety of applications to mesons and baryons.