Fred Sanger, the inventor of the first protein, RNA and DNA sequencing methods, has traditionally been seen as a technical scientist, engaged in laboratory bench work and not interested at all in intellectual debates in biology. In his autobiography and commentaries by fellow researchers, he is portrayed as having a trajectory exclusively dependent on technological progress. The scarce historical scholarship on Sanger partially challenges these accounts by highlighting the importance of professional contacts, institutional and disciplinary moves in his career, spanning from 1940 to 1983. This paper will complement such literature by focusing, for the first time, on the transition of Sanger’s sequencing strategies from degrading to copying the target molecule, which occurred in the late 1960s as he was shifting from protein and RNA to DNA sequencing, shortly after his move from the Department of Biochemistry to the Laboratory of Molecular Biology, both based in Cambridge (UK). Through a reinterpretation of Sanger’s papers and retrospective accounts and a pioneering investigation of his laboratory notebooks, I will claim that sequencing shifted from the working procedures of organic chemistry to those of the emergent molecular biology. I will also argue that sequencing deserves a history in its own right as a practice and not as a technique subordinated to the development of molecular biology or genomics. My proposed history of sequencing leads to a reappraisal of current STS debates on bioinformatics, biotechnology and biomedicine.