Nuclear magnetic resonance spectroscopy (NMR) provides a rich source of structural information which when combined with other spectroscopic data allows structural elucidation of complex compounds as well as a universal detection method for compounds of interest in complex mixtures. NMR is a nondestructive technique that facilitates its coupling with other spectroscopic methods such as mass spectrometry. The key to on-line NMR detection is the design of the flow probe. Suitable probes for continuous flow, stop flow, loop collection, solid-phase extraction, and microflow probes are described emphasizing their general applications and limitations. Sensitivity and probe volume are major limitations of NMR coupling to liquid chromatography. Solvent selection for separations needs to consider the unique characteristics of NMR, for example the use of deuterated solvents for proton detection, and methods available for solvent suppression. Practical applications of LC-NMR are presented to illustrate the use of this technique in different areas of analytical chemistry.