Since Warren Weaver coined the term “molecular biology” in the late 1930s, technological innovation has driven the life sciences, from the analytical ultracentrifuge to high-throughput DNA sequencing. Within this long history, the invention of recombinant DNA techniques in the early 1970s proved to be especially pivotal. The ability to manipulate DNA consolidated the high-profile focus on molecular genetics, a trend underway since Watson and Crick’s double-helical model in 1953. But the ramifications of this technology extended far beyond investigating heredity itself. Biologists doing research on a wide variety of molecules, including enzymes, hormones, muscle proteins, RNAs, as well as chromosomal DNA, could harness genetic engineering to copy the gene that encoded their molecule of interest, from whatever organism they worked on, and put that copy in a bacterial cell, from which it might be expressed, purified, and characterized. Many life scientists who wanted to use recombinant DNA techniques were not trained in molecular biology. They sought technical know-how on their own in order to bring their labs into the vanguard of gene cloners. Manuals became a key part of this dissemination of expertise.