I present a theory of the current-voltage characteristics of diffusive SNS junctions. This theory is based on a solution of the time-dependent Usadel equations, which allows us to describe the phase-coherent transport for arbitrary length of the normal wire. We show how the interplay between proximity effect and multiple Andreev reflections gives rise to a rich subgap structure in the conductance in good agreement with existing experiments. Additionally, I will present the prediction of a novel physical phenomenon that may occur in a mesoscopic conductor coupled to several superconducting terminals. This phenomenon, which is intimately related to the occurrence of MARs in such a system, consists in the possiblity of inducing the so-called Shapiro steps in the absence of any external radiation simply by tuning the voltages of.