Theory and Modeling of MHD Turbulence in Accretion Disks

I will review our current understanding of MHD turbulence in accretion disks driven by the magnetorotational instability.  I will highlight recent progress that has been made in our understanding of protostellar disks, where departures from ideal MHD are important.  I will also discuss the astrophysical implications of the many numerical studies showing a strong dependence of the turbulence level on magnetic Prandtl number.  I will conclude with a discussion reduced models of MHD turbulence, relating them to changes in accretion state.