String theory became a hot subject in the mid-1980s when it became clear that it might give a deeper understanding of the origins of the standard model and a consistent quantum theory containing gravity. Two of its essential ingredients include supersymmetry and extra dimensions of space. Over the years, thanks to efforts of many clever people, we have learned a great deal about the strong-coupling behavior of string theory, the role of nonperturbative excitations called branes, and various dualities. These have led to a rich variety of possibilities for making contact with particle physics phenomenology and cosmology.