The global nitrogen cycle is being rapidly transformed by human activities, including the combustion of fossil fuels, increased agricultural demand, and inefficient nitrogen use. This has led to significant nitrogen losses to air, water, and land, causing environmental and health problems. While some regions have excess nitrogen, others lack it, highlighting global inequalities. The nitrogen cycle's transformation requires an integrated approach to optimize nitrogen use and minimize negative impacts. Since 1970, reactive nitrogen (Nr) production has increased by 120%, driven by agricultural intensification and industrial activities. Nr creation continues to rise, with agricultural activities and fossil fuel combustion playing major roles. From 1860 to 1995, Nr production increased from ~15 Tg N to 156 Tg N, and from 1995 to 2005, it increased further to 187 Tg N yr⁻¹. Cultivation-induced biological nitrogen fixation and industrial uses of Nr also contribute to the cycle. International trade of nitrogen-containing products has increased, leading to concentrated nitrogen inputs in ecosystems. This raises questions about who bears the environmental costs of nitrogen use. Atmospheric transport and deposition have become the dominant distribution mechanism for Nr, with significant impacts on ecosystems. Nitrogen deposition rates have increased dramatically, exceeding natural levels and posing risks to ecosystems. The nitrogen cycle's transformation presents complex challenges, including the need to balance Nr benefits with its environmental impacts. Research is needed to understand Nr's fate, its climate effects, and its impact on human health. Key questions include the ultimate fate of Nr, its net climate effects, and how tropical regions will respond to increased Nr inputs. Biofuel development is altering the nitrogen cycle, with potential to increase Nr emissions. Strategies to reduce Nr losses include controlling NOx emissions, improving crop nitrogen-use efficiency, enhancing animal management, and improving sewage treatment. These interventions could reduce Nr creation by up to 53 Tg N yr⁻¹, helping to offset future increases in Nr losses. The paper emphasizes the need for an integrated approach to manage the nitrogen cycle, balancing its benefits with environmental and health impacts. It highlights the importance of reducing Nr losses while addressing regional disparities in nitrogen availability. The nitrogen cycle's transformation is a critical challenge for sustainable development.The global nitrogen cycle is being rapidly transformed by human activities, including the combustion of fossil fuels, increased agricultural demand, and inefficient nitrogen use. This has led to significant nitrogen losses to air, water, and land, causing environmental and health problems. While some regions have excess nitrogen, others lack it, highlighting global inequalities. The nitrogen cycle's transformation requires an integrated approach to optimize nitrogen use and minimize negative impacts. Since 1970, reactive nitrogen (Nr) production has increased by 120%, driven by agricultural intensification and industrial activities. Nr creation continues to rise, with agricultural activities and fossil fuel combustion playing major roles. From 1860 to 1995, Nr production increased from ~15 Tg N to 156 Tg N, and from 1995 to 2005, it increased further to 187 Tg N yr⁻¹. Cultivation-induced biological nitrogen fixation and industrial uses of Nr also contribute to the cycle. International trade of nitrogen-containing products has increased, leading to concentrated nitrogen inputs in ecosystems. This raises questions about who bears the environmental costs of nitrogen use. Atmospheric transport and deposition have become the dominant distribution mechanism for Nr, with significant impacts on ecosystems. Nitrogen deposition rates have increased dramatically, exceeding natural levels and posing risks to ecosystems. The nitrogen cycle's transformation presents complex challenges, including the need to balance Nr benefits with its environmental impacts. Research is needed to understand Nr's fate, its climate effects, and its impact on human health. Key questions include the ultimate fate of Nr, its net climate effects, and how tropical regions will respond to increased Nr inputs. Biofuel development is altering the nitrogen cycle, with potential to increase Nr emissions. Strategies to reduce Nr losses include controlling NOx emissions, improving crop nitrogen-use efficiency, enhancing animal management, and improving sewage treatment. These interventions could reduce Nr creation by up to 53 Tg N yr⁻¹, helping to offset future increases in Nr losses. The paper emphasizes the need for an integrated approach to manage the nitrogen cycle, balancing its benefits with environmental and health impacts. It highlights the importance of reducing Nr losses while addressing regional disparities in nitrogen availability. The nitrogen cycle's transformation is a critical challenge for sustainable development.