Many of proteins in the living system express carbohydrate moieties, which mediate molecular recognition involved in cell-cell communication and contribute to folding and quality control of proteins via interactions with intracellular lectins. Although biological importance of glycans expressed on proteins has been widely recognized, little is known about their specific roles from the structural aspect. This deficiency in our knowledge is largely due to the lack of an appropriate methodology to deal with glycoproteins as targets of structural biology. Carbohydrate moieties exhibit microheterogeneities and possess a significant degree of freedom in internal motion, which hampers crystallization or interpretation of electron density. In view of the situation, we have been developing stable-isotope-assisted NMR techniques for structural analyses of glycoproteins. For structural analyses of glycoproteins, it is essential to obtain information concerning their glycoforms in advance, which could be facilitated by multi-dimensional HPLC mapping. Based on these data, stable-isotope-assisted NMR spectroscopy could provide us with information concerning dynamical structure of glycoproteins at atomic resolution. By the combined use of these techniques, we monitored conformational changes of immunoglobulin G induced upon removal of the carbohydrate moieties. Interactions between glycoproteins and intracellular lectins involved in folding and quality control of glycoproteins were also studied.