The transfer of mass from one component of a binary system to its companion can involve ejection of the mass by radiation pressure, by Roche lobe overflow, by centrifugal action through the coupling of the upper atmosphere to the stellar rotation through magnetic fields, and by the dynamics of the atmospheric fluid under the action of an energy source at the photosphere or lower chromosphere. I will primarily address the latter mechanism, which commonly goes under the title of stellar winds. The major determinant of a stellar wind is the energy source. In the case of a binary system, the dynamic effects of the system on the flow pattern, particularly for close binaries, is a second major determinant, once an energy source is available to drive the wind.

In addition to ejection, the transfer of mass requires capture of the ejected matter by the companion. The first issue is free particle vs. continuum flow. I will only consider continuum flow, as I doubt the applicability of the free particle concept to any binary system with significant mass transfer, because of the scale height and because of the likely presence of magnetic fields in the interstellar plasma. For more distant binaries, rather simple considerations show that the capture of matter for continuum flow can be enhanced over that for free particle flow.