Turbulence is essential to many fundamental processes in protoplanetary disks, including angular momentum transport, dust evolution, and planet migration. I will focus on two instabilities that can drive turbulent motions in outer disks. In the first part of this talk, a series of global 3D non-ideal MHD simulations via Athena++ code will be presented. The outer disk is found to be weakly MRI turbulent, and annular substructures arise due to magnetic flux concentration. The weak MRI turbulence permits the growth of the vertical shear instability. In the second part of this talk, the saturation of the vertical shear instability mediated via a parametric instability will be covered. Once the parametric instability prevails, it is anticipated that the vertical shear instability is far more incoherent than extant published simulations suggest. Finally, I will touch on a new topic I recently started to work on - debris disk gas evolution.