2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/204642This talk describes the reasons why $η$ and $η^\prime$ decays are an interesting topic of study for both theory and experiment. The main part discusses the results of the recent calculation of $η\to3π$ at two-loop order in ChPT. Some puzzling aspects of the results compared to earlier dispersive calculations are highlighted. I also like to remind the reader of the use of $η$ and $η^\prime$ decays for studying the anomaly.10 pages, {Plenary talk given at MENU07, September 10-14, 2007 Jülich, GermanyNuclear TheoryHigh Energy Physics - Phenomenologytext