Recent studies on the early stages of decomposition in laboratory-prepared Al-Cu and Al-Cu-Mg supersaturated alloys is presented, The fall potential of PALS and two-detector DB techniques for the detection of vacancies and solute aggregates containing open-volume defects is discussed. The kinetics of solute clustering, during the early stages of aging at moderate temperatures, the role of the minority alloying elements and the formation process of vacancy-solute aggregates is discussed. Special emphasis is addressed to the analysis of the effect of the temperature and of the duration of aging on the content of solute atoms in the environment of the vacancies, which survive in the alloy after the initial solution treatment at high temperature, In this framework, it is shown that the kinetics of formation of solute aggregates can be described, after scaling, by a temperature-independent function. Estimates of the solute migration energy in the above mentioned systems are also presented.