Denitrification plays an important role in ecosystem nitrogen (N) cycling, leading to ecosystem N loss and completing the N cycle. It, therefore, has been the subject of hundreds of studies that seek to elucidate controls on the production of its three gaseous end-products, nitric oxide (NO), nitrous oxide (N₂O) and dinitrogen (N₂) gas, in terrestrial ecosystems. These end-products have vastly different impacts on air quality and climate change: NO is a precursor to smog and a key component of acid rain, N₂O is a powerful greenhouse gas and depletes stratospheric ozone, and N₂ is inert and environmentally benign. Despite knowledge gains from individual studies on how variables, such as moisture, oxygen, carbon, inorganic N, pH, and microbial community composition influence denitrification rates and the partitioning of the N gases, we have failed to create a unifying framework for understanding controls on denitrification that can be generalized across terrestrial ecosystems. This session will bring together perspectives from microbiologists, biogeochemists, ecosystem ecologists, and modelers to explore what challenges have hindered advances in our understanding of denitrification and innovative approaches that can overcome these challenges.