After getting his PhD, he stayed in Munich as an assistant and a lecturer between 1965 and 1968. Then, he moved to the Technical University of Hannover where he worked as Professor and Director from 1968 to 1973. In 1973, Professor Ertl returned to the Ludwig Maximilian University of Munich to work as a professor at the Institute of Physical Chemistry. He worked there until 1986 and during this time was a regular visitor to the California Institute of Technology, the University of Wisconsin-Milwaukee and the University of California, in Berkeley where he worked as a visiting professor. In 1986, he became professor at the Free University of Berlin and the Technical University of Berlin. He was director at the Fritz Haber Institute of the MPG from 1986 and was also a professor at the Humboldt University of Berlin from 1996. Professor Ertl retired in 2004.