The Symposium on Predictability of Mesoscale Phenomena (DM3), held at the 1983 IUGG General Assembly, addressed two questions: (1) What mechanisms control the predictability of mesoscale phenomena, in particular quantitative precipitations? (2) Over what time interval can these events be predicted? The papers presented were related more to the first question than to the second. Two sessions were organized. Session I was reserved for the meso-α type studies and session 2 for the meso-β type studies. Space does not permit discussion of all contributions.