This study aims to examine the circumstances under which different types of regional integration lead to convergence and growth, and how such integration could best be fostered. It covers regions across the world, but focuses on developing country regions and Africa in particular. Factors which appear to affect convergence and divergence of incomes within regions include: integration of monetary policy, harmonization policy, different institutions and trading rules; labor mobility; reactions to shocks; macroeconomic convergence; competitive advantage; and homogeneity of the group. Size of the group does not matter.