This chapter provides a framework for the phenomenological study of mental disorders. The framework relies on a distinction between (ontological) existentials and (ontic) modes. Existentials are the categorial structures of human existence, such as intentionality, temporality, selfhood, and affective situatedness. Modes are the particular, concrete phenomena that belong to these categorial structures, with each existential having its own set of modes. In the first section, the chapter articulates this distinction by drawing primarily on the work of Martin Heidegger—especially his study of the ontological structure of affective situatedness (Befindlichkeit) and its particular, ontic modes, which he calls moods (Stimmungen). In the second section, the chapter draws on a study of grief to demonstrate how this framework can be used when conducting phenomenological interviews and analyses. In the concluding section, the chapter explains how this framework can guide phenomenological studies across a broad range of existential structures.