Lise Meitner (November 7, 1878 in Vienna, Austria October 27, 1968 in Cambridge, England), was a German physicist who studied radioactivity and nuclear physics.

Lise Meitner was the third of eight children of a Jewish family. She entered the University of Vienna in 1901, studying physics under Ludwig Boltzmann. After she achieved doctorate degree, she went to Berlin in 1907 to study with Max Planck and the chemist Otto Hahn. She worked together with Hahn for 30 years, each of them leading a section in Berlin's Kaiser Wilhelm Institute for Chemistry. Hahn and Meitner collaborated closely studying radioactivity, with her knowledge of physics and his knowledge of chemistry working in tandem.

In 1918, they discovered the element protactinium.

In 1923, she discovered the radiationless transition known as the Auger effect, which is named for Pierre Auger, a French scientist who discovered the effect two years later.

After Austria was annexed by Germany in 1938, Meitner was forced to flee Germany for Sweden, She continued her work at Manne Siegbahn's institute in Stockholm, but with little support. Hahn and Meitner met clandestinely in Copenhagen in November to plan a new round of experiments. The experiments which provided the evidence for nuclear fission were done at Hahn's laboratory in Berlin and published in January 1939. In February 1939, Meitner published the physical explanation for the observations and named the process nuclear fission.

In 1945, Hahn was awarded the Nobel Prize for physics, and Meitner was ignored by the Nobel committee. This was partially corrected in 1966, when Hahn and Meitner together were awarded the Fermi Prize.

Element 109 is named meitnerium in her honor.