Although theoreticians have developed an array of tools for exploring agency and directionality in living systems, new work is needed to augment and enhance the toolkits available for researchers, especially to represent new biological phenomena. Formal models provide precision for prediction, measurement, and intervention to understand the dynamics of purposive behavior and how it manifests under particular conditions. Generating these models requires interdisciplinary thinking at the intersection of different formal modeling strategies and a deep knowledge of biology. Modeling agency formally can help to open up the space of possibilities, suggest new experimental regimes, and revise our conceptualization of what to expect of the entities and processes of living systems at multiple levels of organization.