ESDU 84015 provides a graphical method for predicting the drag and lift (that is, crosswind force) on each of a pair of closely spaced equal diameter cylinders having their axes parallel and normal to the flow. The method was derived from a correlation of experimental results extracted from the literature and applies to spacings between the axes in the range from one (cylinders touching) to 50 diameters for a range of incidences of 0 to 90 degrees (that is for cylinders in tandem round to cylinders side-by-side). The cylinders can be smooth up to moderately rough, and the Reynolds number range is from 1E4 to 1E6. The data can be used for pairs of pipes, cables, masts, or cylindrical structural members directly, and, using correction factors for finite length and shear flow effects in ESDU 81017, can also be applied to stacks and towers. Also included are descriptions of the flow mechanisms, caused by interference between the flows around the cylinders, which lead to the forces on the cylinders differing from those on an isolated cylinder.