Globally, the quantity of nitrogen (N) fertilizer applied to crops is growing rapidly as it replaces the shrinking contribution of soil organic N and meets the demand by higher-yielding crops. On average, crops recover close to half the applied N, so its inefficient management is an increasing problem. Low nitrogen-use efficiency (NUE) leads to accumulation of mineral N in the soil and thence to pollution of groundwater, streams, oceans and atmosphere. Many management practices are known to increase NUE, and their effectiveness is shown by increasing NUE in Western Europe and the US. In the rest of the world there is no evidence of increasing NUE. Farmers in many regions are adopting improved fertilizer-management practices, but their effect is offset by reduced NUE at higher N rates. The most significant steps to optimising NUE are reducing subsidies that encourage overfertilization and promoting as many cost-effective improved practices as possible.