Abstract: Gauge theories, such as the one describing strong interactions, contain string-like excitations. String theory describes the quantum dynamics of strings and it reduces to gravity at long distances. The simplest versions of string theory live in a ten dimensional spacetime. We will explain how these ten dimensional strings are intimately connected to the strings that appear in four dimensional gauge theories. The four dimensional gauge theory gives rise to a gravitational theory in a higher dimensional curved  spacetime. The gravitational theory is simple to analyze when the four dimensional theory is strongly interacting. This provides a simple way of studying strongly coupled  phenomena en quantum field theories.  In addition, it can be used to describe black holes in a fully quantum mechanical fashion.