In many control applications the reference-to-output map has an extremum and the control objective is to regulate the output close to this extremum. The main objective in extremum seeking control is to force the solutions of the closed loop system to eventually converge to a set in the state space where its output achieves an extremum and to do so without precise knowledge about the reference-to-output map. While this is an old topic, local stability of a class of extremum seeking controllers was proved for the first time by Krstic and Wang in 2000. We have extended these results and proved semiglobal-practical stability of the same class of extremum seeking controllers under natural assumptions. Currently, we are concentrating on robustness analysis of extremum seeking controllers.