ESDU 94026 discusses the behaviour of the lift-curve of an aerofoil depending on its thickness/chord ratio, and the effects on that behaviour of the deployment of high-lift devices. It provides an introduction to and a link between ESDU 84026 which predicts lift at zero incidence and maximum lift for the basic aerofoil with high-lift devices undeployed and the series, ESDU 94026 to 94031, which deals with the incremental effects of deployment of the various types of leading-edge and trailing-edge devices. The method of incorporating the incremental effects is explained and illustrated with a worked example, and the applicability and accuracy of the method is discussed.