We applied a combination of 15 N relaxation and CSA/dipolar cross-correlation measurements at five magnetic fields (9.4, 11.7, 14.1, 16.4, and 18.8 Tesla) to determine the 15 N chemical shielding tensors for backbone amides in protein G in solution. The data were analyzed using various modelindependent approaches and those based on Lipari-Szabo approximation, all of them yielding similar results. The results indicate a range of site-specific values of the anisotropy (CSA) and orientation of the 15 N chemical shielding tensor, similar to those in ubiquitin. Assuming a Gaussian distribution of the 15 N CSA values, the mean anisotropy is -173.9 to -177.2 ppm (for 1.02-Å NH-bond length) and the site-so-site CSA variability is ±17.6 to ±21.4 ppm, depending on the method used. This CSA variability is significantly larger than derived previously for ribonuclease H or recently, using "metaanalysis" for ubiquitin. Standard interpretation of 15 N relaxation studies of backbone dynamics in proteins involves an a priori assumption of a uniform 15 N CSA. We show that this assumption leads to a significant discrepancy between the order parameters obtained at different fields. Using the sitespecific CSAs obtained from our study removes this discrepancy and allows simultaneous fit of relaxation data at all five fields to Lipari-Szabo spectral densities. These findings emphasize the necessity of taking into account the variability of 15 N CSA for accurate analysis of protein dynamics from 15 N relaxation measurements.