Until now, glycosylation chemistry has still been dominated by the concept of Koenigs-Knorr glycosylation. The glycosyl oxocarbenium ion is accompanied with a counterion as an ion pair, which may exist as a close-contact ion pair (CCIP), a solvent separated ion pair (SSIP), and/or a covalent glycoside adduct. This chapter discusses the effect of solvent on glycosylation with respect to the physical properties of the solvent. A binary or quaternary solvent system contains two or more solvent components and is common in glycosylation. Based on the polarity and electron-pair-donating capacity, the chapter classifies the solvents used in glycosylation to weakly polar and noncoordinating solvents such as benzene and toluene; moderately polar and noncoordinating solvents such as CH2Cl2, CH3NO2, and C2H4Cl2; highly polar and coordinating solvents such as CH3CN and EtCN; and weakly polar and coordinating solvents such as diethyl ether (Et2O) and dioxane. The effects of these solvents in glycosylation are also described.