Diagrams figure prominently in human reasoning, especially in science. Cognitive science research has provided important insights into the inferences afforded by diagrams and revealed differences in the reasoning made possible by physically instantiated diagrams and merely imagined ones. In scientific practice, diagrams figure prominently both in the way scientists reason about data and in how they conceptualize explanatory mechanisms.To identify patterns in data, scientists often graph it. While some graph formats, such as line graphs, are used widely, scientists often develop specialized formats designed to reveal specific types of patterns and not infrequently employ multiple formats to present the same data, a practice illustrated with graph formats developed in circadian biology . Cognitive scientists have revealed the spatial reasoning and iterative search processes scientists deploy in understanding graphs.In developing explanations, scientists commonly diagram mechanisms they take to be responsible for a phenomenon, a practice again illustrated with diagrams of circadian mechanisms. Cognitive science research has revealed how reasoners mentally animate such diagrams to understand how a mechanism generates a phenomenon.