The Sanctuary is a marine area of 87,500 sq. km subject to an agreement between Italy, Monaco and France for the protection of marine mammals, which live in it.

What makes the Pelagos Sanctuary for Mediterranean Marine Mammals unique is the fact that it is a site managed by three different authorities and includes coastal areas and international waters that form a large ecosystem of major scientific, socio-economic, cultural and educational interest. The entire Sanctuary can be broadly considered to be a biogeographically distinct sub-section of the Large Marine Ecosystem (LME) that is the Mediterranean.

This sub-section is marked by greater productivity caused by a variety of mechanisms of fertilization enhancing the level of primary production: coastal waters, the delayed effect of winter mixing, the frontal area, upwelling phenomena and complex structures that combine divergent and convergent features.

A rough estimate lists more than 8,500 macroscopic animal species representing between 4 % and 18 % of global marine species, a remarkable biodiversity, particularly with regard to the number of predators at the top of the food chain such as marine mammals, since Mediterranean represents only 0.82 % of the area and 0.32 % of the volume of the world's oceans.

However, the biodiversity within this sub-section of the Marine Ecosystem of Great Dimension Mediterranean undergoes the combined pressure of natural environmental fluctuations and human impacts.