Recently, several experimental collaborations have invested considerable
effort into new and more precise measurements of the eta -> 3 pi decays.
These experimental advances require revisiting the corresponding
theoretical analyses. In this talk, we present a new calculation of the
eta -> 3 pi decay amplitude relying on dispersive methods. We show how the
study of this decay allows one to extract a fundamental parameter of the
Standard Model, namely the quark mass ratio
(m_d^2-m_u^2)/(m_s^2-\hat{m}^2), with good precision. We then discuss the
possibility of extracting the individual light quark masses.