  In this contribution, we briefly analyze the formalism of the unquenched
quark model (UQM) and its application to the calculation of hadron spectra with
self-energy corrections, due to the coupling to the meson-meson continuum. In
the UQM, the effects of $q \bar q$ sea pairs are introduced explicitly into the
quark model through a QCD-inspired $^{3}P_0$ pair-creation mechanism. The UQM
formalism can be extended to include also the effects of hybrid mesons, i.e.
hybrid loops. The main applications to spectroscopy and decays are analyzed.
