Process tracing theorists have offered rich and inspiring accounts on social causation in the last twenty years. In this chapter, we analyze the sense in which singular causality is in line with the idea of the causal chain connecting causes and outcomes. We hold that this is a realist conception of causation that is appropriate for the practice of biographical research. We focus on the concept of “casing” as a key to crafting causal hypotheses regarding the causal processes that make things happen and that explain the phenomenon of interest. Furthermore, we underline through sociological examples how Mackie’s theory of causality enables biographical researchers to identify the scope conditions of the causal field they bring to the fore in investigating social phenomena.