 One might think that diagrams are only important as a means of illustrating results that are presented textually. But examination of the practices of scientists reveals that they are far more central to their reasoning. Early in the development of a mechanistic hypothesis scientists sketch their ideas. Often mechanism diagrams (as well as the other figures that show data or the workflow of the research) are crafted long before text is drafted. Diagrams are commonly presented in lab meetings and revised multiple times as scientists are refining their claims. Researchers often generate the text of the paper only at the end of this process. Taking advantage of access to the draft figures and text for two research projects, Sheredos and Bechtel (2017, in press) examined the process of interactive engagement in which the investigators modified diagrams, changed text, and then further modified the diagram. What this process suggests is that sketching and resketching mechanisms plays a central role as researchers seek to identify what they can conclude from their experimental studies. In one of the cases they examined, an early version of a diagram serves to pose a question that was addressed through the experimental studies, resulting in a final diagram that offers an answer to the question posed. Beyond supporting the empirical claims of a research project, Jones and Wolkenhauer (2012) provide an illuminating discussion of how diagrams serve to locate information required for a computational model in a representation of the cellular mechanism that is being modeled,