We shall begin by introducing different kinds of mental states, and by clarifying some of the central and prima facie unique features of the mental. We shall then present the mind-body problem, and discuss central theories regarding the nature of mental states and their ontological status: dualism, behaviorism, the identity-theory, functionalism and the computer model of the mind. We shall also discuss following issues, which stand at the core of current discussions in philosophy of mind: consciousness, mental content and mental causation.