  Heavy ion collisions (HIC) at high energies are excellent ways for producing
heavy hadrons and composite particles. With upgraded detectors at RHIC and LHC,
it has become possible to measure hadrons beyond their ground states.
Therefore, HIC provide a new method for studying exotic hadrons that are either
hadronic molecular states or compact multiquark systems. Because their
structures are related to the fundamental properties of QCD, studying exotic
hadrons is currently one of the most active areas of research in hadron
physics. Experiments carried out at various accelerator facilities have
indicated that some exotic hadrons may have already been produced. The present
review is a summary of the current understanding of a selected set of exotic
particle candidates that can be potentially measured in HIC. It also includes
discussions on the production of exotic hadrons in HIC based on the coalescence
and statistical models. A more detailed discussion leads to the conclusion that
the yield of a hadron is typically an order of magnitude smaller when it is a
compact multiquark state than that of an excited hadronic state with normal
quark numbers and/or a molecular configuration. Attention is also given to some
of the proposed heavy exotic hadrons that could be produced with sufficient
abundance in HIC because of the significant numbers of charm and bottom quarks
produced at RHIC and LHC, making it possible to study them in these
experiments. Further included in the discussion are the general formalism for
the coalescence model that involves resonance particles and its implication on
the present estimated yield for resonance production. Finally, a review is
given on recent studies to constrain the hadron-hadron interaction through
correlation measurements in HIC and their implications on the interpretation
and the possible existence of exotic states in hadronic interactions.
