Abstract: The brief biography of Hans Geiger is outlined. His research of the radioactivity under the guidance of Ernest Rutherford, especially the alpha-particle scattering experiment which he made with Marsden is reviewed. How he developed and improved his counters and how he researched the Compton effect with Bothe by coincidence method are introduced. Geiger＇s outstanding style of work is discussed.

Key words: Hans Geiger, Ernest Rutherford, Geiger-Marsden experiment, Geiger counter, coincidence method