Max Delbrück (September 4, 1906 - March 9, 1981) was a German biologist.

He was born in Berlin, Germany. His father was Hans Delbrück, a professor of history at the University of Berlin, his mother was the granddaughter of Justus von Liebig.

Delbrück studied astrophysics, shifting towards theoretical physics, at the University of Göttingen. After receiving his Ph.D., he traveled through England, Denmark, and Switzerland. He met Wolfgang Pauli and Niels Bohr, who got him interested in biology. Delbrück went back to Berlin in 1932 as an assistant to Lise Meitner.

In 1937, he moved to the United States, taking up research at Caltech on genetics of the fruit fly Drosophila melanogaster. Delbrück stayed in the US during World War II, teaching physics at the Vanderbilt University in Nashville.

In 1939, he co-authored a paper called The Growth of Bacteriophage with E.L. Ellis in which they demonstrated that viruses reproduce in "one step ", rather than exponentially as cellular organisms do.

In 1941, he married Mary Bruce, with whom he had four children.

In 1942, he and Salvador Luria demonstrated that bacterial resistance to virus infection is caused by random mutation and not adaptive change. For that, they were awarded the Nobel Prize in Physiology or Medicine in 1969, sharing it with Alfred Hershey.

From the 1950s on, Delbrück worked on physiology rather than genetics. He also set up the institute for molecular genetics at the University of Cologne.

See also: Luria-Delbruck experiment