His research interests span several areas in condensed matter physics, including electronic and photonic nanostructures (electronic states and radiation-matter interaction in semiconductor heterostructures, excitons and polaritons in microcavities, photonic crystals) and strong correlations (Kondo systems). His most significant works concern binding energies and the radiative recombination of excitons in quantum wells, radiation-matter interaction and polariton states in semiconductor microcavities, and more recently the theory of photonic crystal waveguides and of intrinsic and disorder-induced losses in these systems. His theoretical research is characterized by a close relation with experiments, as shown by the numerous works in collaboration with Italian and foreign experimental groups. Since about 2000 his research activity is largely focused on nanophotonics, especially photonic crystals, concerning both the theory and the interpretation of optical experiments performed in Pavia and in other laboratories. More recently, this research evolved into activities related to photovoltaics, silicon photonics, plasmonics, chiral photonics.