The coasts are animated by a particularly dynamic force, due to natural processes that confer intrinsic mobility, sometimes increased by human actions. In addition, the acceleration of the contemporary level rise on the seas and oceans is a sign of the future accentuation of this mobility. However, when in resonance with social issues, this dynamic becomes a source of coastal risks. On the one hand, the coastline tends to retreat toward the land. On the other hand, settlements have become more concentrated near the sea. Both these natural evolution and human occupation have resulted in a predictable "telescoping" over the century. These converging dynamics are at the source of the emergence and proliferation of the risks associated with the mobility of the coastline. It tends to spread to most urbanized coastlines in the world. Today, the critical cases of buildings destroyed by erosion or flooding are still outstanding on the French coast, but they are expected to grow as the density of buildings along the coast could not be completely controlled by policies for coastal management. It is therefore urgent to consider a long term strategy, offering several options depending on the characteristics of these spaces. Despite a system of actors and tools, and a general doctrine quite clearly established, the management of coastal risks in France poses many problems on the ground. We note that, in practice, hasty decisions, lack of communication or outright opposition impede sustainable management of the shore. These obstacles also originate in constructions which are already built regardless of any sustainable development consideration. Today, their protection raises concern. Regarding prevention, and therefore the future and future generations, the difficulties come mainly from differences in spatial and temporal scales in risk assessment, the interweaving of issues involving the public and private interests, and thus ultimately difficulties of articulation between local and global levels. In any case, whatever the strategy (strengthening the defense against the sea or managed retreat), recognition of the coastline as a territory at risk is a key point to any policy prevention and rational management. Keywords: risk, vulnerability, coastal, erosion, flooding, management, strategies, France, French Guiana