ESDU Aero A.S.02.03.01 indicates that the basis of the area rule is the fact that, within certain limitations, the flow around a wing-body combination at zero incidence may be represented by a source distribution that is the streamwise derivative of its cross-sectional area. The limitations are that the body is smooth and slender, the wing is thin and has sharp edges, and the drag due to wing/body interference is negligible. The equation for the drag is given together with the form it reduces to when Mach number approaches unity which yields the theoretical transonic drag rise. Reference is made to other sources for methods of calculating the drag rise and the optimum area distribution. The equation for the drag according to the transfer rule is then given and the terms in it explained. It may be used to find the optimum area distribution at a particular Mach number or over a range of Mach numbers, and is also applicable to wing-body combinations with discontinuities provided they do not occur in the region defined by planes normal to the stream at the foremost and rearmost points of the wing. Reference is again made to other sources for methods of calculating some of the terms. The equation for drag according to the moment of area rule is then introduced and it is noted that it offers a method of optimising the area distribution at supersonic speeds. A bibliography of sources of both theoretical and experimental studies is included. The process of calculating the transonic drag rise by area rule methods is illustrated in ESDU Aero A.02.03.02.