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. We 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. Roche lobe overflow might be thought of as a limiting case in which the system dynamics predominate.