Glycosylation is the most abundant post-translational modi fi cation of proteins. Estimates
vary widely, but a common assessment is that upwards of 50% of eukaryotic proteins are
modi fi ed by some type of glycan. Indeed, the dif fi culties associated with accurately assessing
the glycosylation status of intra- and extracellular proteins are the primary motivations for
this volume. Over the past 30 years, insight into the biological roles of glycan modi fi cations
has grown dramatically, yet this fi eld has often struggled due to the inadequacies of accessible
analytical methods. Fortunately, simultaneous to the recent expansion of knowledge
in glycobiology, a similar transformation has occurred in the fi eld of glycoproteomics. New
enrichment techniques, novel ionization methods, mass spectrometry technologies, the
expanding role of high-performance liquid chromatography, and improved informatic
resources have transformed niche characterization of discrete glycoproteins into a powerful
“omics” toolset that can simultaneously characterize diverse glycoproteins and the glycans
they carry. Although proteomics approaches have been applied to broad classes of posttranslational
modi fi cations, glycoproteins represent a particularly challenging case due to
the heterogeneity of glycan structures, the lability of glycosidic bonds, the isobaric nature
of many monosaccharides, and the dif fi culties associated with determining the unique
structure of a branched molecule from compositional analysis. As presented in this volume,
the latest glycoproteomics tools are meeting these challenges, providing unprecedented
information about the structure and diversity of glycoproteins. It is an exciting time to be
both a glycobiologist and mass spectrometrist