In this chapter, a brief introduction to the basic theory of nuclear magnetic resonance (NMR) spectroscopy is presented, including the quantum mechanical and classical description (using the vector model) of magnetic resonance, spin-relaxation processes and nuclear overhauser effects, and a brief discussion about the spectroscopic parameters extracted from the NMR spectrum. A short account on the different pulses and basic pulse sequences used in one- and two-dimensional NMR is given. Two-dimensional NMR spectroscopy covers a large part of this chapter. It includes the basic principles, a detailed description of the correlation spectroscopy experiment and the modes of the presentation of two-dimensional NMR spectra. The most useful two-dimensional NMR experiments for food scientists are presented and discussed. Finally, this chapter contains a short description of the basic principles underlying solid-state NMR, magnetic resonance imaging and time domain NMR.