The application for surface sensitive analytic techniques to the study of grain boundary diffusion in thin films is described. Two common experimental configurations, sputter profiling and permeation analysis, are described, as are solutions for data reduction. Analytic solutions are difficult to use, even with simplifying assumptions. Rather, a versatile numerical method for data reduction, the method of lines, is used to analyze concentration profiles and surface accumulation concentrations. Both analytic and numerical calculations are compared to data for chromium diffusing in gold and the grain boundary half‐width times diffusion coefficient (cm3/sec) is shown to be 8.6 ×10−11 exp(−25000/RT).