In the five southern countries of the EU, the mountain and disadvantag
ed regions cover a huge area (56 million hectares, 27 million inhabita
nts). The main trends are demographic and economic decline. Neverthele
ss, there are signs of potential resistance to marginalization. The ME
DEF network has studied nineteen such cases. This paper compares the f
indings of the case studies, in particular with respect to the externa
l and internal factors determining the success of local initiatives fo
r development. It shows that success depends on the types of resources
mobilized, mechanisms of valorization, marketing strategies and the e
ffects of public assistance.