One of the authors (Kimihiko Hirao) was invited to the University of Tokyo in 1993 as the first professor of theoretical chemistry. Since then, our quantum chemistry research group has grown larger and larger and has now become one of the centers of theoretical chemistry in Japan. We are aiming at developing accurate molecular theory on systems containing hundreds of atoms. We continue our research in the following three directions: (i) development of new ab initio theory, particularly multireference-based perturbation theory; (ii) development of molecular theory including relativistic effects; and (iii) development of exchange and correlation functionals in density functional theory. We have enjoyed good progress in each of the above areas. We are very excited about our discoveries of new theory and new algorithms and we would like to share this enthusiasm with readers. The present review is a summary of our research activities achieved in the last 5 years.