This interdisciplinary work contains the most sustained attempt at developing and defending one of the few genuine theories of consciousness. Following the lead of David Rosenthal, the author argues for the so-called 'higher-order thought theory of consciousness'. This theory holds that what makes a mental state conscious is the presence of a suitable higher-order thought directed at the mental state. In addition, the somewhat controversial claim that "consciousness entails self-consciousness" is vigorously defended. The approach is mostly 'analytic' in style and draws on important recent work