[en] The paper reviews in detail the effects of microalloying and comments on the origins of hardening in age-hardenable Al alloys. The review focuses on 2000 and 7000 series alloys because these have been the subjects of particularly active alloy development in recent times. It will be shown that advances in the techniques of atom probe field ion microscopy and transmission electron microscopy are providing new insights into the decomposition processes in these alloys and that the nature and kinetics of the precipitation process depend critically on pre-nucleation phenomena. We summarise recent experimental observations of solute-solute-vacancy interactions, which produce solute clusters. These precede the formation of precipitation, including GP zones and have a defining role on the nature and kinetics of the subsequent precipitation processes. We show indirect evidence, based on observations of defect structure and hardening, that the type and dispersion of clustering can be controlled by changing the free vacancy content and/or the number density of vacancy sinks in the microstructure. Finally, we further discuss the interaction between dislocations and solute clustering, which seems to produce a significant hardening effect, the origins of which are distinctly different from the conventional notion of precipitation hardening