Key Points: The use of stable isotope analysis in grassland science has increased enormously in the last two decades. It is providing insight into the functioning of grassland systems, including aspects such as the biogeochemical cycles of carbon, nitrogen and water, C 3 :C 4 vegetation dynamics, the nutritional ecology of grassland fauna, and the (agro)ecology of cattle production systems. This paper deals with the natural stable isotope compositions of three major bioelements (carbon, nitrogen and oxygen) and how they behave in organisms and ecosystems, and it describes examples of recent research progress in the ecology of grassland systems, which were made with the help of stable isotope analysis. Introduction Until 1990 stable isotope analysis was used only sporadically in grassland research. Today, more than 6% of all 'grassland' publications appearing in the ISI Web of Science data base employ stable isotope analysis. Several reviews and books have been published in the last years, which covered various aspects of the application of natural stable isotope analysis in ecology and in the study of stable isotope behaviour in the environment and in organisms (e.g
