Biological diversity is a concept that has been developed and enshrined in multilateral agreements in a very short space of time. It is generally agreed that it was in 1986 that the concept was introduced. Much older in concept is cultural diversity. These two diversities are now meeting each other in many ways, not least through Multilateral Environmental Agreements (MEAs). And both diversities are recognised, explicitly and implicitly, as part of the global heritage of humankind, with the attendant responsibilities that flow from that. In this paper we show the extent to which the two diversities are mutually self-supporting, and yet how in many cases MEAs seem to have ignored their mutual strengths. However, the very needs that are promoting synergies between the MEAs and broader UN programmes are also now promoting new ways of viewing interaction between the diversities. Nowhere is this clearer than in cultural landscapes, which feature explicitly in some MEAs but have impacts in all. For the future some seven key areas of research and development will help to build the strengths and mutual interaction of the diversities, within the policy framework of the MEAs.