Solution nuclear magnetic resonance spectroscopy is usually only used to study proteins with molecular weight not exceeding about 50 kDa. This size limit has been lifted significantly in recent years, thanks to the development of labelling methods and the application of transverse-relaxation optimized spectroscopy (TROSY). In particular, methyl-specific labelling and methyl-TROSY have been shown to be effective for supramolecular systems as large as about 1 MDa. In this chapter we review the available methods for labelling different kinds of methyl groups and the assignment strategies in very large protein systems. Several proteins are selected as examples to show how NMR helps to reveal the details of structure, interaction and dynamics of these proteins.