Interfacial interdiffusion in quantum wells and superlattices could alter the interfacial strain, band alignment, and even the atomic symmetry at the interface, thus potentially changing the electronic and optical properties. We consider-the InAs/GaSb system describing the interdiffused interfaces via a simple kinetic model of molecular beam epitaxy growth. The predicted atomic positions after interdiffusion are then used in a pseudopotential theory to describe the electronic and optical consequences of interdiffusion. We determine (i) the effects of different interfacial bonding compositions on the electronic and optical properties; (ii) the segregation profiles at the normal and inverted interfaces; and (iii) the effect of structural disorder on band gaps. The application of our method to the InAs/GaSb superlattices allows us to explain numerous observed results and trends.