N. Turner (Jet Propulsion Laboratory, California Inst of Tech, Pasadena, United States),
S. Fromang (CEA Saclay, France),
C. Gammie (University of Illinois, Urbana-Champaign, Astronomy Department, United States),
H. Klahr (MPIA Heidelberg, Germany),
G. Lesur (Inst of Planetology and Astrophysics Grenoble, France),
M. Wardle (Macquarie University, Physics and Astronomy Department, Australia),
X. Bai (Harvard-Smithsonian Center for Astrophysics, United States)

Planets appear to form in environments shaped by the gas flowing through protostellar disks to the central young stars. The flows in turn are governed by the transfer of orbital angular momentum. Here we summarize current understanding of the transfer processes best able to account for the flows, including magneto-rotational turbulence, magnetically-launched winds, vortices driven by hydrodynamical instabilities, and self-gravitational instability. For each process in turn we outline the major achievements of the past few years and the outstanding questions remaining. We underscore the requirements for operation, especially ionization for the magnetic processes, and heating and cooling for the processes driven by gas pressure forces. We describe the distribution and strength of the resulting flows and compare with the long-used phenomenological alpha-picture, highlighting issues such as grain transport and heating where the newer and more-detailed models yield substantially different answers. We also discuss the links between magnetized turbulence and magnetically-launched outflows, and between magnetized turbulence and hydrodynamical vortices. We end with a review of the prospects for detecting specific signatures of the flows in the next few years.

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