  An accurate line list for calcium oxide is presented covering transitions
between all bound ro-vibronic levels from the five lowest electronic states \X,
\Ap, \A, \astate, and \bstate. The ro-vibronic energies and corresponding
wavefunctionts were obtained by solving the fully coupled Schr\"{o}dinger
equation. \textit{Ab initio} potential energy, spin-orbit, and electronic
angular momentum curves were refined by fitting to the experimental frequencies
and experimentally derived energies available in the literature. Using our
refined model we could (i) reassign the vibronic states for a large portion of
the experimentally derived energies [van Groenendael A., Tudorie M., Focsa C.,
Pinchemel B., Bernath P. F., 2005, J. Mol. Spectrosc., 234, 255], (ii) extended
this list of energies to $J=79-118$ and (iii) suggest a new description of the
resonances from the \A--\X\ system. We used high level \textit{ab initio}
electric dipole moments reported previously [Khalil H., Brites V., Le Quere F.,
Leonard C., 2011, Chem. Phys., 386, 50] to compute the Einstein A coefficients.
Our work is the first fully coupled description of this system. Our line list
is the most complete catalogue of spectroscopic transitions available for
$^{40}$Ca$^{16}$O and is applicable for temperatures up to at least 5000~K. CaO
has yet to be observed astronomically but its transitions are characterised by
being particularly strong which should facilitate its detection. The CaO line
list is made available in an electronic form as supplementary data to this
article and at \url{www.exomol.com}.
