Water is vital to all life processes. In foods, water is often the key component which determines the extent and rate of several chemical reactions, as well as the growth of microorganisms. There are several methods available to measure water content in foods; however, one of the most successful methods is Nuclear Magnetic Resonance (NMR) spectroscopy. The NMR method is rapid and accurate and, most importantly, non-destructive to the sample. The purpose of this chapter is to discuss the use of NMR, both as a research tool and as a quality control (off- and on-line) method, to measure moisture content in food components and food systems.