Johannes Geiss (4 September 1926 – 30 January 2020) was a German physicist.

He published his doctoral thesis in 1953, titled Isotopenanalysen an „gewöhnlichem Blei“.

From 1958 to 1959, Geiss was an associate professor at the University of Miami before returning to Bern, working there until 1991.

At Bern he devised the Solar Wind Composition Experiment for the Apollo program to measure the isotopic and elemental composition of noble gases in the solar wind.

In 2019, a bronze statue of Geiss was erected on the University of Bern campus by Horst Bohnet.