Stahl, Franklin William (1929-) is an American geneticist and expert in the field of bacteriophages, parasitic viruses that multiply within their host bacteria. He is well known for elucidating the replication process of dioxyribonucleic acid (DNA) in bacteria, a discovery he made in collaboration with chemist Matthew Meselson.

Stahl became interested in genetics, and in particular the genetics of bacteriophages, while taking a course at New York's Cold Spring Harbor Laboratories, after completing his undergraduate work at Harvard in 1951. While he was enrolled as a graduate student at the University of Rochester, he spent his summers working at Cold Spring Harbor with A. H. Doermann, an acclaimed bacteriophage researcher. In 1956, after obtaining his Ph.D. degree in biology, Stahl began post-doctoral research at the California Institute of Technology (CalTech).

At CalTech, Stahl first encountered Meselson, another graduate student, and together they designed an experiment to discover the replication process of bacterial DNA. Early attempts failed but when they tried their process using the bacteria Escherichia coli, the experiment was successful. Replication was found to be a “semi-conservative” process, that is, the two strands of the double helix of bacterial DNA are separated and from each of those “parent” strands a new “daughter” DNA molecule forms, each having an “old” strand identical to its parent strand and one strand of newly synthesized DNA. Because, in the new daughter DNA molecules, exactly half of the original genetic material is saved, or “conserved,” it is known as a semiconservative process. This discovery laid the foundation for tremendous further advancements in molecular biology.

Since this discovery, Stahl has done much further research into genetic bacteriophages and has shared his knowledge as professor and researcher at many prestigious institutions throughout the world.