The chapter addresses whether the critical load of nutrient nitrogen (N) is a relevant, necessary and sufficient indicator to address adverse effects of reactive nitrogen (Nr) on biodiversity in different regions of the world. Based on a description of the critical loads concept for nutrient N, and the relationship to biodiversity endpoints, applications of the critical load for nutrient N are summarized in the context of policies under the Long-range Transboundary Air Pollution (LRTAP) Convention. Potential applications of critical loads are addressed with respect to the relevance of adverse effects of N under the Convention on Biological Diversity (CBD). The chapter considers the prospects for effect-based applications in different regions of the world and poses some questions that need to be addressed. Finally, the potential for a broader indicator for N (a ‘threshold’ rather than a ‘load’) that could apply to all forms and impacts of N is considered, as it could potentially increase the coherence between CLRTAP and CBD.