  The past decade witnessed the observation of several exotic charmonium-like
resonances, some of which are manifestly non-qqbar mesons. We review one of the
most popular interpretations of such states: the compact tetraquark in the
constituent diquark-antidiquark picture. Moreover, we discuss some unexplored
decay channels which are particularly sensitive to the different
phenomenological models and could therefore shed some light on the nature of
these fascinating states. Some brief comments on the recently observed
pentaquarks are also included.
