<p>Self-illness ambiguity (SIA) has been understood, roughly, as a difficulty in delineating one’s self from one’s mental illness. In this paper, we explicate some of the previously neglected complexity of SIA, by distinguishing two forms of the phenomenon: (a) identity-related SIA (<i>‘How do I relate to my illness?’</i>) and (b) agential SIA (<i>‘Is it me or my illness that makes me act/think/feel a certain way?’</i>). In addition, we differentiate general and particular varieties of these SIA-forms, as well as descriptive and analytic approaches to them. The resulting taxonomy allows (1) clarifying the growing SIA-literature, (2) supporting (self-)understanding in clinical contexts, and (3) drilling into the normatively significant features of SIA, e.g., enabling the better theorising of potential connections between agential SIA and questions of responsibility. Our taxonomy thus strengthens the conceptual foundation for future theories and applications of SIA.</p>