The Galactic halo, above and below the Galactic disk, is filled with gas
at ~1-3 million K. This gas is a major contributor to the diffuse soft
X-ray background (SXRB) in directions looking out of the Galactic disk. 
Despite many years of study, the origin of the hot halo gas remains
uncertain. X-ray spectroscopy of the SXRB emission enables us to
determine the physical conditions in the hot gas, providing clues to its
origin and evolution.

We have recently completed a survey of the SXRB using data from the  
orbiting XMM-Newton X-ray observatory. I will describe how we use the 
data from this survey to measure the halo's X-ray emission, and how we  
are using these results to test physical models for the origin of the
hot gas.