In recent years, canopy reflectance sensing has been investigated for in-season assessment of crop nitrogen (N) health and subsequent control of N fertilization. The several sensor systems that are now commercially available have design and operational differences. One difference is the sensed wavelengths, although these typically include wavelengths in both the visible and near-infrared ranges. Another difference is orientation – the sensors most commonly used in the US are designed to operate with a nadir (vertical) view of the crop, while some sensors developed in Europe and now becoming available in the US are designed to view the crop obliquely. Data comparing the different sensor designs is lacking. Thus, the objective of this research was to evaluate three different commercial canopy reflectance sensors for N fertilization control in corn. Two units of each of three commercial sensors – Green Seeker, Crop Circle, and Topcon – were mounted to a high-clearance applicator for field data collection. The sensors were operated according to manufacturer recommendations – two in a nadir orientation and one viewing the corn canopy from an angle. Data were collected from five field experiments in 2009. Multiple blocks of randomized N rate response plots traversed each field. Each block consisted of 8 N treatments from 0 to 235 kg N ha^-1, side-dressed between vegetative growth stages V7 and V11. Crop canopy reflectance sensor measurements were obtained from the N response blocks at the time of side-dress N application. At one site, additional sensor measurements were obtained over a range of growth stages after N application. Data will be analyzed to determine how closely each sensor tracked variations in corn N health and economically optimal N rate. This research is expected to provide information that can be used to select appropriate sensor technologies for variable-rate corn N fertilization on farmers’ fields.