The object of the present paper is to draw attention to some of the recent researches which have had as object the improvement of the aerodynamic characteristics of aircraft. Such characteristics can be classified into two groups; those concerned with performance and those concerned with stability and control. In the former group come all those researches which aim at the reduction of drag, while in the latter group come those directed to the attainment of satisfactory stability and control in normal flight, as well as those concerned with the behaviour of auxiliary devices such as flaps and slots which are used under special conditions and in particular during landing and taking-off. The problems associated with flutter also belong to this group. The two groups may be broadly characterised by the words economy and safety.