We investigate self-ascriptions of psychological states, such as “I wish that the sun were shining,” “I believe that it is raining,” and “I am in pain,” and claim that they are expressions, rather than descriptions, of our own mental states. Our main aim is to develop a systematic theory of psychological expressivism. Yet psychological expressivism is also of great significance beyond the confines of the philosophy of language. We explore consequences for epistemology (transparency of belief, self-knowledge), for the philosophy of mind and self (dualism, two uses of “I”), and for the history of philosophy (Descartes’ Cogito and Kant’s “I think”).