Over the past twenty years, significant advances in statistical mechanics have provided engineers with accurate equations of state for bulk phase behavior of mixtures containing associating, polar, and polymeric components. More recently, developments in statistical mechanics are providing scientists and engineers with valuable tools to correlate and predict bulk and interfacial phase behavior and microstructure of complex systems containing block copolymers and surfactants. Insights will be provided in the development of these theories. Opportunities for applications and extension of these models also will be discussed along with future challenges.