The use of carbohydrates as drugs and vaccines has several limitations. Molecular mimics of carbohydrates provide an alternative source of compounds to target pathways involving protein-carbohydrate interactions. In recent years, immunological studies have demonstrated the ability of certain peptides to act as molecular mimics of carbohydrates, in that they are able to induce an anti-carbohydrate immune response. Carbohydrate-mimetic peptides that bind to enzymes and lectins have also been discovered. The nature of this mimicry at the molecular level is currently the subject of investigation. Structural data regarding the origin of mimicry are reviewed, and their implications for drug and vaccine design are presented.