My research focuses on understanding the nonperturbative aspects of gauge and string theories. To this end, the most powerful tools are gauge/ gravity duality and localization. The localization principle allows the path integral of a theory to be reduced into a matrix integral, and some exact results in strongly coupled field theories to be computed. It thus gives very precise predictions for the gauge/gravity duality. I utilize the combination of these ideas in order to understand the microscopic origin of the black hole entropy.