This book provides a rigorous treatment of spectral analysis using Fourier-based techniques in the geosciences, specifically geodesy and geophysics that deal with global and regional spatial data. It emphasizes spatial -frequency analysis for data on the plane and sphere. It includes applications to stochastic processes on the plane and sphere, which are important for many estimation problems that are based on some kind of stochastic constraints in inverse theory. It also briefly outlines wavelet analysis, although unusual, it is included to illustrate the contrast to traditional spectral analysis, going more toward a time-frequency analysis.