Colourless Mesons in a Polychromatic World

The N_C → ∞ limit of QCD gives a useful approximation scheme to the physical hadronic world. A brief overview of the mesonic sector is presented. The large-N_C constraints on the low-energy chiral couplings are summarized and the role of unitarity corrections is discussed. As an important illustration of the 1/N_C expansion techniques, the Standard Model prediction of ɛ'/ɛ is reviewed.