A rigorous multicomponent isotherm for preparative immobilized metal affinity chromatography (IMAC) must consider the multipointed nature of adsorption, the possibility of steric hindrance of the stationary phase upon binding of macromolecules, and the role of the mobile-phase modifier. In this paper, the metal affinity interaction chromatography (MAIC) model, a formalism which addresses all three of these issues, is presented. The linear and nonlinear adsorption behavior of proteins as a function of mobile-phase imidazole content is considered. Numerical simulations of nonlinear chromatography, employing MAIC equilibrium, are seen to accurately predict the experimental results in various modes of nonlinear IMAC chromatography. In frontal chromatography, the model is seen to accurately describe the adsorption phenomena, including induced imidazole gradients. In step gradient and displacement chromatography, the results presented in this manuscript demonstrate the ability of the MAIC model to predict multicomponent equilibrium in IMAC systems and establish this model as a powerful tool for studying the operation of IMAC separations.