THE recent synthesis of silica-based mesoporous materials(1,2) by the cooperative assembly of periodic inorganic and surfactant-based structures has attracted great interest because it extends the range of molecular-sieve materials into the very-large-pore regime. If the synthetic approach can be generalized to transition-metal oxide mesostructures, the resulting nanocomposite materials might find applications in electrochromic or solid-electrolyte devices(3,4), as high-surface-area redox catalysts(5) and as substrates for biochemical separations. We have proposed recently(6) that the matching of charge density at the surfactant/inorganic interfaces governs the assembly process; such co-organization of organic and inorganic phases is thought to be a key aspect of biomineralization(7). Here we report a generalized approach to the synthesis of periodic mesophases of metal oxides and cationic or anionic surfactants under a range of pH conditions. We suggest that the assembly process is controlled by electrostatic complementarity between the inorganic ions in solution, the charged surfactant head groups and-when these charges both have the same sign-inorganic counterions. We identify a number of different general strategies for obtaining a variety of ordered composite materials.