This chapter contains sections titled: Context Clues and Constraints Local Magnetohydrodynamic Instabilities in Disks Numerical Simulations Dynamo Theory The Incoherent Dynamo in Astrophysical Disks Summary Context Clues and Constraints Local Magnetohydrodynamic Instabilities in Disks Numerical Simulations Dynamo Theory The Incoherent Dynamo in Astrophysical Disks Summary