Eta and Eta' physics

This talk describes the reasons why $\eta$ and ${\eta }^{\mathrm{\prime }}$ decays are an interesting topic of study for both theory and experiment. The main part discusses the results of the recent calculation of $\eta \to 3\pi$ 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 ${\eta }^{\mathrm{\prime }}$ decays for studying the anomaly.