Gregor Möller demonstrates comprehensively that tomography principle, as commonly used in medicine for diagnostic purposes, can be well applied to signals of the global navigation satellite system (GNSS). With the newly defined approach, wet refractivity fields can be generated which coincide with radiometer and radiosonde measurements significantly better than operational weather models. This makes GNSS tomography interesting for meteorological applications in particular, but also for other disciplines, which relay on accurate modeling of the signal delay in the lower atmosphere. The book assesses all relevant parts of GNSS tomography, from electromagnetic wave propagation and GNSS signal processing over tomography theory to specific test cases and applications.