Hydrophilic interaction chromatography (HILIC) with mass spectrometry is a versatile technique for structural glycomics. Glycans are retained by hydrogen bonding, ionic interactions, and dipole-dipole interactions. Glycopeptides as well as glycans with various modifications and reducing-end labels can be efficiently separated, which often results in the resolution of isobaric species. Chromatography is usually performed with solvent mixtures of organic modifier (often acetonitrile) and volatile (acidic) buffer which are suitable for online-electrospray ionization-mass spectrometry. When performed at the nano-scale, this results in a detection limit for oligosaccharides of approximately 1 femtomol. Alternatively, glycans may be analyzed by offline-MALDI-MS(/MS) in both negative-ion mode and positive-ion mode, which allows the registration of informative fragment ion spectra from deprotonated species and sodium adducts, respectively. (c) 2009 Wiley Periodicals, Inc., Mass Spec Rev 28:192-206, 2009.