The aim of the World Heritage Convention is to ensure the protection for all time of the world's natural and cultural heritage of Outstanding Universal Value. In 1994, to assist in meeting this aim, the World Heritage Committee adopted a Global Strategy for achieving a balanced, representative and credible World Heritage List that reflects the world's diverse heritage. Over the past 10 years a number of studies and consultations have been carried out to develop and refine the Global Strategy. This review is an important addition to that process, focusing on the inter-related elements of biogeography, habitats and biological diversity that underpin much of what we consider 'natural heritage'. Two of the four criteria by which Natural World Heritage Sites can be nominated relate respectively to ecological and biological processes, and to the in-situ conservation of biological diversity. Understanding the relative values and importance of global biomes, habitats and biological diversity is therefore extremely important in ensuring that new nominations are evaluated on a scientifically sound basis. The availability and application of such knowledge is important in the first place to States Parties as they consider what properties to place on their national Tentative Lists of potential World Heritage nominations and in making the case for inscription in their nominations. It is essential information also for IUCN, as the Advisory Body to the Convention on Natural World Heritage in its evaluation of nominations.