This article addresses two approaches to flood risk prevention in France: the first is institutional in nature and government managed; the other is local in nature and under the authority of territorial communities. Great emphasis is placed on risk in institutionalized government prevention. This normative approach defines one type of risk for all territories. Managed locally, risk is defined in terms of everyday perceptions. Risk at this level is territorially-based, and prevention must therefore consider other kinds of logic. Both approaches do not draw on the same criteria of rationalization and knowledge of risks. The first approach argues that major risks are entirely unacceptable, but when experienced at the local level, they involve making difficult compromises between the presence of risk and the need for land-use planning. Flood-risk prevention in France is chiefly founded on an institutional, government managed approach that does not embrace local knowledge of risk. As a result, the implementation of flood prevention policy is characterized by dissonance.