 One of the central objectives of many philosophers of science focused on mechanistic explanations is to characterize reasoning strategies or heuristics that scientists use to develop mechanistic explanations (Bechtel &amp; Richardson 1993 [2010]; Craver &amp; Darden 2013; Gross 2018). We discuss reasoning strategies that figure in different phases of developing mechanistic explanations in cell biology: delineating phenomena and situating them in responsible mechanisms, identifying and characterizing the components of mechanisms (a reductionistic phase), and determining the organization within mechanisms and between mechanisms and their contexts (a more holistic phase).