Carbohydrates covalently linked to proteins and to lipids also occur at the surfaces of membranes. They are, in fact, primary mediators in processes that involve interaction of a cell with its external environment. These include important processes such as cell-cell interactions, hormone stimulation, and invasion by pathogens. Structural characterization of the carbohydrate moieties in their native environment is essential to understanding and controlling the processes in which they are involved. Many of the NMR methods being developed to characterize membrane proteins are equally applicable to cell surface carbohydrates In addition, methods that are more focussed at the details of protein-carbohydrate recognition interactions are important. A number of lectins from plant and animal sources are being studied as models for these recognition processes, and as a testing ground for methods that can characterize them.