The marine World Heritage thematic study was written to provide guidance to States Parties and conservation practitioners on how to best apply the World Heritage Convention in the oceans and seas. The study proposes a scientific framework as the foundation for a well-balanced and representative set of features that may be of Outstanding Universal Value to inform choices when nominating or inscribing sites. It also analyses the current biogeographic coverage of marine World Heritage sites (mWHS) and identifies broad gaps in representation.