Glycosyltransferases are enzymes that transfer sugars from nucleotide sugars to a wide range of small molecule acceptors, from hormones and secondary metabolites to biotic and abiotic chemicals. This alters the hydrophilicity of the acceptors, their stability and chemical properties, their subcellular localization and often their bioactivity. Glycosyltransferases form a large multigene family in the plant kingdom and can be identified by a signature motif in their primary sequence. Considerable progress has been made in understanding the biochemistry of glycosyltransferases and the role of these enzymes in the plant. This article outlines our current knowledge of these enzymes, drawing on information gained from recent in vitro and in planta studies.