Since man has been trying to fly, a war against drag been engaged. At the present time, drag reduction is an industrial challenge in Aeronautics which justifies the efforts devoted to this topic. One facet of these efforts deals with the skin-friction drag reduction. Two directions are followed. The first one is the manipulation of turbulent boundary layers. By altering the formation of turbulence or by modifying its characteristics it is hoped to decrease the turbulent skin-friction. The second direction concerns the action on laminar-turbulent transition. By delaying the occurrence of the turbulent regime enormous skin friction reductions are possible. This Lecture Series on Skin-Friction Drag Reduction is aimed at giving an overview of the state of the art on the various means which are being studied to obtain significant gains.