  The hadronic decays eta' -> eta pi pi are studied in the frameworks of
large-Nc Chiral Perturbation Theory, at lowest and next-to-leading orders, and
Resonance Chiral Theory in the leading 1/Nc approximation. Higher order effects
such as pi-pi final state interactions are taken into account through a
detailed unitarization procedure. The inclusion of finite-width effects in the
case of RChT is also discussed. The Dalitz plot distribution and the
differential branching ratio are computed in both approaches. The predicted
Dalitz plot parameters obtained from the different treatments are compared with
the most recent measured values. We find that the eta' -> eta pi pi branching
ratios are easily understood, while the Dalitz plot parameters require the
inclusion of pi-pi loops in order to achieve a reasonable agreement. Our final
predictions agree with the experimental measurements. We hope our results to be
of relevance for present and future experimental analyses of these decays.
