Eta and Eta' physics

Abstract

This talk describes the reasons why $\eta$ and $\eta^\prime$ decays are an interesting topic of study for both theory and experiment. The main part discusses the results of the recent calculation of $\eta\to3\pi$ 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 $\eta$ and $\eta^\prime$ decays for studying the anomaly.Comment: 10 pages, {Plenary talk given at MENU07, September 10-14, 2007 J\"ulich, German