Mark Davis grew up in Pittsburgh, Pennsylvania, the second of five children. His father was a civil engineer, his mother an architect. Davis took an early interest in science, thanks to wide reading and an influential high school biology teacher. Davis matriculated at Johns Hopkins University. Trouble in a mini organic chemistry class sent him to Peter Johnson's synthetic organic chemistry lab, where he helped produce two papers. He switched majors to biology because he thought it answered important questions. He worked in Michael Beer's lab, trying to sequence DNA with a transfer scanning microscope. Hopkins was known for its membrane biologists, and Davis, interested in molecular biology, wanted to combine the study of DNA with classical genetics studies. He consulted his advisors, who told him to take a physical chemistry class and suggested graduate studies at California Institute of Technology (Caltech). There he went into Edward Lewis' Drosophila lab, but he hated flies and found Lewis difficult to work with. He then went to Eric Davidson's lab, where he worked with Glen Galau and William Klein on sea urchins. Davidson was harshly critical and Davis found the lab atmosphere oppressive; he moved to Leroy Hood's lab. There he worked successfully with Philip Early, an early molecular biologist. Davis cloned the first mouse genomic library. His approach to science is to prepare thoroughly, to avoid what others do, and to look for variations. Davis's next move was to National Institutes of Health. In William Paul's lab he designed a general technology to find genes expressed at very low levels. At Ronald Schwartz's suggestion Davis used pulse field gel technology to discover delta chain of T-cell receptors. Recognizing that T-cell receptors are important for immunology, Davis, the only molecular biologist in his department, began his work on T-cell receptors, work that continues today. Davis still works in his lab, which is beginning to do biochemical work on T-cells, trying to engineer expression of membrane proteins in soluble form. His lab is also working with transgenic mice, a more difficult system for which he gets help from Pamela Bjorkman and others. Davis applies to science the strategies of fencing; he compares the principles of economy and mastery in fencing to samurai movies.