  Scores of exotic hadrons, particularly tetraquarks and pentaquarks in the
heavy-quark sector, have been observed in the past 20 years, and more continue
to be discovered to this day. Unlike mesons and baryons, such exotics are not
mandated to exist under our current understanding of QCD, meaning that each new
discovery presents fresh insights into the expansive possibilities of
strong-interaction physics. Even the basic architecture of these multiquark
states remains an open question. Here we discuss the merits and deficiencies of
their best-known dynamical descriptions, recognizing that the eventual
universal model for exotics will almost certainly require the synthesis of more
than one fundamental paradigm.
