While the progress of science has been described by some as proceeding by a series of “crucial experiments,” I claim that an important factor in the development of many scientific fields is that of what I call “crucial resolutions” of outstanding anomalies. In contrast to crucial experiments, crucial resolutions are proposed to solve persistent anomalies or conflicting theoretical positions – often in advance of experimental confirmation. I illustrate this point using specific examples from the history of endocrinology. I claim this general structure of explanatory models can serve as a template for philosophical and historical investigations in other scientific fields.