Fostering young people's commitment to protect biodiversity is an important goal of Education for Sustainable Development (ESD) in both, industrial countries and designated biodiversity hotspots. However, little empirical evidence exists to describe factors that influence such commitments. Based on the Value-Belief-Norm (VBN) theory, 15 to 19-year-old Chilean (n=216) and German (n=217) pupils' commitment to protect biodiversity was investigated. Comparisons revealed that Chilean adolescents showed higher personal norms and commitments to protect biodiversity. Regression analysis showed that within the German sample, the "Schwartz"-value universalism was an important predictor for three different kinds of behavioural commitment. In both samples, "ascription of responsibility", "perceived ability to reduce threat" and, above all, "personal norms" were positive predictors. The paper concludes with a discussion of the results in the light of existing evidence and suggests implications for biodiversity education. (Contains 1 figure and 4 tables.)