Basic features of the superstring picture of the microworld are discussed. This picture suggests that there is a certain nonlocal object--the string--in many-dimensional (D = 10, 26, 506) space-time on the scale of the Planck length (10$^{-33}$ cm). Transition to larger scales gives rise to the localization and compactification of the theory. The result is an effective supersymmetric low-energy theory combining all fundamental interactions, including gravity.