This thesis discusses the emergence of a new concept of ‘law' at global level in the field of sustainable development which is mainly inspired from the process leading to the adoption of the Sustainable Development Goals (SDGs). Based on Hart's concept of law and Tamanaha's ‘non-essentialist legal pluralist perspective', the thesis provides an examination of the four-decade-long evolution of the concept of sustainable development starting from the Stockholm Conference of 1972 until the adoption of the SDGs in 2015. The thesis illustrates, step by step, how the proposed concept of 'law' was affirmed at global level by relevant actors. In that sense, the originality and the main contribution of the thesis to the broadest understanding of what is ‘law' at global level is to bring forward a step-by-step guide for exploring law-like quality of global norms from a legal positivist and legal pluralist perspective.