While a variety of biophysical techniques are available to characterize biomolecular interactions, very few can fully address complex interactions such as those involving simultaneous self- and hetero-association or multivalent interactions. Composition-gradient multi-angle light scattering (CG-MALS) is uniquely suited to tease out and quantify the binding affinity and molecular stoichiometry of complexes that occur in these systems. We present examples of CG-MALS characterization of multivalent association and the metacomplexes that form when both binding partners are bivalent, including IgG binding to a dimeric Fcg receptor; an aptamer that binds to two sites on streptavidin; and an anti-streptavidin IgG that binds two apparent sites on streptavidin.