According to ordinary intuition, living individuals and organisms are the same thing. Developments in the life sciences, however, have indicated that familiar organisms are just one case of individuality among others, including genes, cells, colonies, groups, species, and even ecosystems. It has therefore become a problem to explain what it is, in general, that makes something a biological individual. My project takes its point of departure from the insufficiency of evolutionary explanations currently on offer, in which being an individual roughly means being a unit of selection. Instead of opposing this by recourse to more physiological explanations of individuality, however, I suggest it will be more illuminating to integrate both within a more general hierarchical framework. I propose to do this by introducing into the discussion a dynamical or process-based view of both individuation and hierarchical organization. A dynamical perspective ensures that biological individuation is explained as an ongoing, evolving process. A hierarchical perspective is necessary for accommodating the fact there are different dynamics at different levels and scales that are causally responsible for individuating biological systems. Carrying out this project will involve developing an alternative to the dominant approaches to biological hierarchy theory that relies on dynamical parameters and pervasive scalar properties of the living world. I also connect the issues of biological individuality and hierarchy to wider concerns about the explanatory power of natural selection, problems with biological functionalism, and the relationships between biology and the other natural sciences.