To systematically study the static stability for airplanes, we proposed the system of definitions of six static stability concepts. The details of “static flight speed stability” and “static angle of attack stability” were discussed in the first report of this paper, and “static pitch stability” was studied in the second. In this third report, the static stability concepts of lateral and directional motions are discussed, and their stability criteria are obtained in terms of the aerodynamic characteristics of an airframe. They are “static sideslip stability,” “static roll stability,” and “static yaw stability,” and their fundamental definitions are respectively “dY⁄dβ 0” for static roll stability, and “Cnβ>0” for static yaw stability, respectively, as the criteria in normal and low subsonic flights. As a conclusion, a summary of this entire paper is given.