The purpose of this report is to explain and illustrate methods of calculating the deflection of beams of nonuniform section. The application of these methods to airplane analysis is given in article 173 of Structural Design and Analysis of Airplanes. All methods of computing the deflection of beams are based on the fundamental differential equation of the elastic curve of a beam under load. It should be thoroughly understood that the deflections obtained by these methods are deflections from a tangent to the elastic curve of the beam. This is not generally true of the deflection formulae found in the handbooks.