I review studies of the hot gaseous medium in and around nearbynormal disk galaxies, including the Milky Way. This medium represents a reservoir of materials required for lasting star formation, a depository of galacticfeedback (e.g., stellar mass loss and supernovae), and an interface between the interstellar and intergalactic media. Important progress has been made recently with the detection of X-ray absorption lines in the spectra of X-ray binaries and AGNs.The X-ray absorption line spectroscopy, together with existing X-rayemission and far-UV O iv absorption measurements now allowsfor the first time to characterize the global spatial, thermal, andchemical properties of hot gas in the Galaxy. The results aregenerally consistent with those inferred from X-ray imaging of nearby edge-on galaxies similar to the Milky Way.Observed diffuse X-ray emitting/absorbing gas doesnot extend significantly more than ~10 kpc away from galactic disks/bulges, except in nuclear starburst or very massive galaxies. The X-ray cooling rate of this gas is generally far less than the expected supernova mechanical energy input alone. So the bulk of the energy is “missing”. On the other hand, evidence for alarge-scale (≲ 102 kpc) hot gaseous halo around the Milky Way to explain varioushigh-velocity clouds is mounting. The theoretical argument for ongoing accretion of intergalactic gas onto disk galaxies is also compelling. Idiscuss possible solutions that reconcile these facts.In particular, large-scale hot gaseous halos appear to be low inmetallicity, hence X-ray emission. The metal enrichment in theintergalactic medium may be substantially non-uniform; fast-cooling clumps ofrelatively high metallicity may have largely dropped out and may partly account for high-velocity clouds. In addition, ongoing galactic mechanical energy feedbackis likely important in balancing the cooling of the halos and may bestrong enough to produce galactic winds in bulge-dominated galaxies.
