The catastrophes occurring in recent years and a changed awareness not only among “experts” but in the whole society of the reasons for hydro-geological calamities are in fact pointing out the urgency of a correct policy for the preven-tion of hydro-geological risk and the development of more adequate systems for forecasting disasters. In the light of a problem of this entity, it is necessary to act on two fronts: careful planning and programming of the use of territorial re-sources, as well as setting up decision making support systems that can improve the efficiency of the actions taken. In this paper the topic of planning in areas with hydro - geological risk is deal with, through the implementation of two different methodologies: the former is a probabilistic - quantitative one for the definition of the hydraulic dangerousness; the latter is a qualitative one (able to consider also social, economic, cultural and political aspects) for the definition of vulnerability considered as the ability of a territorial system to answer to the calamitous events.