Publisher Summary This chapter summarizes the structural and conformational studies of large molecules, particularly those of biochemical importance. The 13C nmr of carbohydrates, nucleic acids and their constituents, proteins and their residues, lipids and macromolecular model systems are discussed. Brief references are made on determinations of 13C spin-lattice relaxation times. Utilization of these methods for obtaining information on molecular motions and interactions is described. The relative simplicity of proton-decoupled C spectra is increasingly being utilized for identification and correlation of polysaccharides obtained from different natural and synthetic sources. Nuclear magnetic resonance studies of amino-acids, peptides, proteins, and lipids are summarized. The chapter states that micellar surfactants and macrocyclic compounds are being extensively investigated as possible models for the more complex enzyme-substrate interactions and catalyses. Substrate solubilization, either by dynamic association with micelles or by incorporation in the cavities of macrocyclic compounds, saturation kinetics, competitive inhibition and some degree of specificity observed in the different systems all support their utility as enzyme models.