Current high nitrogen (N) fertilizer costs and continuing efforts to reduce N losses from cropland have increased interest in use of sidedress or delayed applications in corn production as a method for increasing the effectiveness of applied N and for avoiding adverse environmental impacts from N use. Theoretically, sidedress N has potential for improving N efficiency because N is usually applied just before the period of rapid N uptake by corn so that possible N losses before the application date are avoided. A common expectation is that a lower N rate applied sidedress will achieve the same yield response as a larger amount of N applied earlier in the growing season. Sidedress or delayed N applications have potential allowing reduced N rates only if early season losses of N from preplant applications are significant and can be avoided by applying N later in the growing season. While this is clearly the case on coarse-textured sandy soils where N loss by nitrate leaching from preplant N is likely, the benefits of sidedressing N is less obvious on medium-textured well-drained soils. The purpose of this paper is to review results from research studies and on-farm research and demonstration work that included or evaluated sidedress N applications for corn.