This document discusses mutualization of environmental data and knowledge through metadata and reference bases. It aims to facilitate information exchange between actors by developing common platforms. These platforms include a metadata service to catalog and share resources using standards like ISO 19115. They also provide reference bases like ontologies and thesauri to control vocabularies and spatial objects. This knowledge mutualization helps search and interpret data in its proper context. The goal is to optimize environmental monitoring, management and decision making by enabling easy access and understanding of diverse environmental information sources.