Superstring theory is a promising candidate for the unified theory. That is, superstring theory can provide us with the framework to describe all of interactions including gravity and matter such as quarks and leptons as well as Higgs particle. Indeed, much study has been done to derive realistic aspects of particle physics such as the standard model of particle physics and its extensions like grand unified theories and supersymmetric extensions. Also, cosmological aspects derived from superstring theory have been studied. In this talk, we explain what we have been understanding in string phenomenology and cosmology and also discuss what we should study in future.