  In this paper I summarize the science motivations, as well as a few
mid-infrared spectroscopic methods used to identify the principal mechanisms of
energy production in dust enshrouded galactic nuclei. The development of the
various techniques is briefly discussed. Emphasis is given to the use of the
data which are becoming available with the infrared spectrograph (IRS) on
Spitzer, as well as the results which have been obtained by IRS over the past
two years.
