The most recently published accounts of experimental data relating to the copper-cadmium alloy system are the thermal investigation of Jenkins and Hanson who mapped out the equilibrium diagram, and the X-ray work of Bradley and his collaborators! on the structure of the δ-phase. The present paper gives an account of an attempt to apply X-ray analysis to the whole series, particular attention being paid to alloys in the α-phase, the parameters of which have been measured to a high degree of accuracy. The X-ray methods employed took two forms, namely, powder spectrum analysis and precision camera measurements. The former has been used to make a general survey over the whole range of composition, and the latter, to study in detail the α-phase.