The term “Nature-based solutions” (NbS) has now entered the lexicon of natural resource managers. Yet there is still a lack of clarity regarding what Nature-based solutions offer to a world pining for sustainability. This is shown in sharp relief by the different definitions and positions taken by IUCN and, among others, the European Commission. Although NbS are applicable worldwide the origin of the idea from two European-based agencies has given it a strong Eurocentric focus. Recent literature has expanded the focus to a more global one. Yet, in striving for sustainability in today's world, with rapid and unpredictable change and real questions on how close we are to crossing planetary boundaries (if, indeed, such boundaries exist), we need to resolve what “nature” we are talking about and what “solutions” we see it providing. There are 10 clear, interrelated principles, governed by feedbacks between and among them that can be derived from the thinking behind NbS. These principles echo those of the Ecosystem Approach of the Convention on Biological Diversity and can be linked to the whole theoretical and practical base included under the discipline of Ecohydrology. UNESCO's work in Ecohydrology and Biosphere Reserves under the International Hydrological and Man and the Biosphere Programmes continues to provide practical solutions for global management of water and ecosystems on a rapidly evolving theoretical base. To be fully effective NbS must focus on twenty-first century environmental problems and what solutions nature can contribute in resolving known, known-unknown and unknown-unknown problems.