This paper shows why qualia constitute a problem for any theory of mental phenomena. We use the term ‘qualia’ in reference to non-intentional features of mental states which are eminently qualitative, i.e. perceptions, emotions, moods and body sensations. These non-intentional features are usually described as intrinsic, ineffable, infallible, atomic, private, direct and irreducible to the physical. The paper also explains the absent qualia argument which is addressed as a critique to functionalism.