The atomic interstellar medium is observed to be highly turbulent, and to <br /><br />
contain structure over a wide range of scales in the form of cold fliamentary <br /><br />
clouds embedded within a warmer medium. Recent observations have suggested <br /><br />
that a significant portion of the warm medium may be out of thermal <br /><br />
equilibrium. I will discuss recent numerical models that have investigated the <br /><br />
dynamics and thermodynamics of the atomic gas, focusing on the role of the <br /><br />
magnetorotational instability. The MRI has been extensively studied in the <br /><br />
context of accretion disks, but this is the first detailed study of MRI in a <br /><br />
strongly inhomogenous medium. I will describe the properties MRI-driven <br /><br />
turbulence in atomic gas under a range of galactic conditions, and discuss <br /><br />
implications for understanding various aspects of galactic structure and <br /><br />
evolution.<br /><br />