This is a brief overview on the current status of string theory for
non-specialists. The purpose is to give an aspect on the nature of string
theory as a unified theory of all interactions including quantum gravity and to
discuss future perspectives. Particular emphases are put on the mysteries why
string theory contains gravity and why it resolves the ultraviolet problems.Comment: 19 pages, 1 figure, written version of a general talk in the workshop
"Frontier of Theoretical Physics", Beijing, Nov, 1999, minor typos correcte