Carbohydrates are the basis for many therapeutic and diagnostic strategies, yet the full potential of glycans in medicine has not been realized. The study of the precise role of different carbohydrates, bound to either proteins or lipids, is hampered by difficulties in accessing pure, well-defined glycoconjugates. This Review highlights recent advances in glycobiology with a particular emphasis on oligosaccharide synthesis and conjugation techniques for the construction of homogeneous glycoconjugates. New methods for the study of protein-glycan interactions such as carbohydrate arrays and in vivo visualization of glycosylation pattern changes will also be addressed. The development of glycotherapeutics is just beginning, and much remains to be understood about the relationship between glycoconjugate structure and function. The emergence of novel tools will certainly facilitate and expand the use of carbohydrates in therapeutics and diagnostics.