  Since the discovery of the $J/\psi$, the quark model was very successful in
describing the spectrum and properties of heavy mesons including only $q\bar q$
components. However since 2003, with the discovery of the $X(3872)$, many
states that can not be accommodated on the naive quark model have been
discovered, and they made unavoidable to include higher Fock components on the
heavy meson states. We will give an overview of the success of the quark model
for heavy mesons and point some of the states that are likely to be more
complicated structures such as meson-meson molecules.
