Nitrogen is an essential nutrient for plant growth. In order to increase agricultural productivity (and as an unintended side-effect of fossil fuel use), humans have increased reactive nitrogen inputs to the Earth System by a factor 2–3 over the past century. Next to beneficial effects on crop yields, this has led to adverse effects on the environment and human health. This thesis (further) develops and applies spatially explicit models to assess trade-offs between nitrogen’s benefits for crop production and its environmental impacts in Europe and globally. Models are applied to quantify how much nitrogen can be safely applied in agriculture before crossing regional and planetary boundaries, to what extent better nitrogen management can reconcile environmental targets and food production goals, and how human nitrogen use affects the climate by indirectly enhancing carbon sequestration in terrestrial ecosystems. Outcomes provide policy-relevant indicators on trade-offs in sustainable nitrogen management and can thus be used to support policy0making in Europe and globally.