  I review some selected aspects of the phenomenology of multiquark states
discovered in high energy experiments. They have four valence quarks (called
tetraquarks) and two of them are found to have five valence quarks (called
pentaquarks), extending the conventional hadron spectrum which consists of
quark-antiquark $(q\bar{q})$ mesons and $qqq$ baryons. Multiquark states
represent a new facet of QCD and their dynamics is both challenging and
currently poorly understood. I discuss various approaches put forward to
accommodate them, with emphasis on the diquark model.
