Max Ludwig Henning Delbrück (German: [maks ˈdɛl.bʁʏk] ⓘ; September 4, 1906 – March 9, 1981) was a German–American biophysicist who participated in launching the molecular biology research program in the late 1930s.

Formed in 1945 and led by Delbrück along with Salvador Luria and Alfred Hershey, the Phage Group made substantial headway unraveling important aspects of genetics.

His mother was granddaughter of Justus von Liebig, an eminent chemist, while his father Hans Delbrück was a history professor at the University of Berlin.

Found guilty by the People's Court for roles in the July 20, 1944 plot to assassinate Hitler, Dietrich and Klaus were executed in 1945 by the RSHA.

Though theoretically tenable, his conclusion was misplaced, whereas Hans Bethe some 20 years later confirmed the phenomenon and named it "Delbrück scattering".

In 1939, with Emory L. Ellis,[16][17] he coauthored "The growth of bacteriophage", a paper reporting that the viruses reproduce in one step, not exponentially as do cellular organisms.

[19] The Luria–Delbrück experiment, also called the Fluctuation Test, demonstrated that Darwin's theory of natural selection acting on random mutations applies to bacteria as well as to more complex organisms.

To put this work in its historical perspective, Lamarck in 1801 first presented his theory of Inheritance of Acquired Characteristics, which stated that if an organism changes during life in order to adapt to its environment (for example stretches its neck to reach for tall trees), those changes are passed on to its offspring.

The most elegant and convincing support for Darwin's ideas, however, was provided by the Luria-Delbruck experiment,[20][21][22] which showed that mutations conferring resistance of the bacterium E. coli to T1 bacteriophage (virus) existed in the population prior to exposure to T1 and were not induced by adding T1.

In 1945, Delbrück, Luria, and Hershey set up a course in bacteriophage genetics at Cold Spring Harbor Laboratory on Long Island, New York.

[23] Delbrück received the 1969 Nobel Prize in Physiology or Medicine, shared with Luria and Hershey "for their discoveries concerning the replication mechanism and the genetic structure of viruses".

His inferences on genes' susceptibility to mutation was relied on by physicist Erwin Schrödinger in his 1944 book What Is Life?,[27] which conjectured genes were an "aperiodic crystal" storing codescript and influenced crystallographer Rosalind Franklin and biologists Francis Crick and James D. Watson in their 1953 identification of cellular DNA's molecular structure as a double helix.

On August 26 to 27, 2006—the year Delbrück would have turned 100—family and friends gathered at Cold Spring Harbor Laboratory to reminisce on his life and work.