Dr Gilles BILLEN is a Research Director CNRS (Emeritus), still teaching a course on Territorial Biogeochemistry in the Master ‘Science of the Universe and the Environment” at Sorbonne Université (ex. P. & M. Curie Univ.) in Paris. He played a leading role in the development of biogeochemical modelling tools, aimed at testing scenarios for water resources management. He is now conducting interdisciplinary research devoted to the modelling of nutrient transfer between agricultural land and hydro systems, at various scales from regional or global. He also participated in various international forums and projects, and to editorial teams.