Meselson, Matthew Stanley (1930-), an American molecular biologist, is best known for his experimental confirmation, in collaboration with Franklin William Stahl, of the Watson-Crick theory of DNA replication. According to James Dewey Watson and Francis H. C. Crick, DNA replication is semiconservative: the daughter cells each receive one strand of DNA from the original parent cell and one newly replicated strand.

A liberal arts graduate of the University of Chicago, Meselson completed a doctorate in 1951 and then completed a second doctorate in physical chemistry at the California Institute of Technology (Caltech) in 1957. He remained at Caltech as a research fellow and then joined the faculty in 1958. In 1960, he left for Harvard University, where he remained until 1976. During his final year in graduate school at Cal Tech, he began his collaboration with Stahl, who was a research fellow there in biology. Working with Escherichia coli bacteria (E. coli), the collaborators used a method Meselson designed for analyzing the densities of giant molecules to prove one of the most important concepts in modern molecular biology: that when the double helix of DNA splits into two during replication, each of the DNA molecules contains one strand from the parent molecule and one newly synthesized strand.

He later showed that the splicing of DNA molecules results in genetic recombination—a process by which genes from each parent join to create the offspring's genetic makeup. Before turning his attention to the study of molecular evolutionary mechanisms, he demonstrated that the process by which cells recognize and destroy foreign DNA has an enzymatic basis, and discovered methyl-directed mismatch repair, the process by which cells are able to repair mistakes in DNA.

He is a member of the Committee on International Security and Arms Control of the U.S. National Academy of Sciences and of the Advisory Committee to the Director of the U.S. Arms Control and Disarmament Agency.