The present investigation deals with the boundary layer transition problem in relation to the fundamental aerodynamics of general airplanes. Focus has been especially placed on the mechanism of three-dimensional (3D) boundary layer transition and its control, which is meaningful not only for its fundamental interest but also important in relation to aero- and hydro-dynamic applications. In order to clarify the complicated transition mechanism, both flow visualizations and hot wire measurements are conducted in the transition region of general 3D boundary layer flows, namely, on spinning, yawed, and curved surfaces of the kind that often appear in surfaces of industrial fluid machinery. A unique attempt to delay such transition, applying an effective control method, is also reported.