Studying the behavior of the Kaehler-Ricci flow on mildly singular varieties, one is naturally lead to study weak solutions of degenerate parabolic complex Monge-Ampere equations. I will explain how viscosity methods allow one to define and study the long term behavior of the normalized Kaehler-Ricci flow on mildly singular varieties of positive Kodaira dimension, generalizing results of Song and Tian who dealt with  smooth minimal models. This is joint work with P.Eyssidieux and A.Zeriahi