What is introspection? Does introspection deliver theoretically valuable information about the mind? There is a long history in philosophy and psychology of using introspection to gather data about the mind. Introspection is often held to constitute our best and only direct access to consciousness and hence to be essential to any investigation of the conscious mind. Equally longstanding and widespread, however, are critical concerns that introspection is highly susceptible to interference, which, together with its privacy, renders it unreliable as a source of data about the mind.Maja Spener offers an understanding of introspection that clarifies its epistemic importance in theorising about the mind. In particular, seemingly overwhelming concerns about the reliability of introspection are transformed into something methodologically more tractable. Central to the approach put forward in the book is the distinction between introspection as inquiry and introspection as mental capacity - between introspective method and introspective access. The first part of the book articulates, defends, and applies a novel framework for the systematic assessment of the potential and limitations of introspective methods. The framework is historically motivated, drawing on insights from key figures in early scientific psychology (especially Wilhelm Wundt, William James, and Georg Elias Müller) whose used and discussed introspective methods extensively. The second part of the book develops a composite pluralism about introspective access, showing how different modes of introspective access fit into the common sense and scientific pictures of our minds. Key to this pluralist account is the explanatory role introspection plays in our agency.