Chapter 8 focuses on turbulent boundary layers. This considers a proposed autonomous cycle for turbulence production that results from an instability of a distorted mean flow near the wall surface that is produced by a spanwise array of coherent longitudinal vortices whose spacing scales with the viscous shear stress. The instability results in a lift-up and break-up of the longitudinal vortices that are linked to increased turbulence production and increased viscous drag. This and other mechanisms of turbulence production and viscous drag generation are presented. Methods of flow control that key on these specific mechanisms are presented along with significant results.