Boundary layer transition refers to the phenomenon where fluid shifts from laminar to turbulent flow, causing significant changes in wall friction forces, heat flux, and flight mechanical characteristics. Therefore, accurate transition prediction is crucial for research in aerospace, wind engineering, and related fields. This book will provide comprehensive coverage of development methodologies for subsonic/transonic boundary layer transition models, formulation of Very Large Eddy Simulation (VLES) approaches applicable to separated flows and construction techniques for transitional-separated flow hybrid models.