  The search for mesons with non-quark-antiquark (exotic) quantum numbers has
gone on for nearly thirty years. There currently is experimental evidence of
three isospin one states, the $\pi_{1}(1400)$, the $\pi_{1}(1600)$ and the
$\pi_{1}(2015)$. For all of these states, there are questions about the
identification of these state, and even if some of them exist. In this article,
we will review both the theoretical work and the experimental evidence
associated with these exotic quantum number states. We find that the
$\pi_{1}(1600)$ could be the lightest exotic quantum number hybrid meson, but
observations of other members of the nonet would be useful.
