Field-ion microscopy connected with the successive field-evaporation technique and the atom-probe analysis has been applied to studying precipitation processes, especially the early stage of precipitation, in age-hardenable aluminium alloys, such as Al-Cu, Al-Ag and Al-Sc alloys. In Al-Cu alloys, coexistence of the single-layer G.P.(1) zones and the multilayer G.P.(1) zones has been confirmed and the difference between G.P.(1) zones and G.P.(2) zones has been clearly recognized. In Al-Ag alloys, the octahedral shape of η-G.P. zones has been confirmed. In Al-Sc alloys, it has been found that the equilibrium Al3Sc phase particles precipitate homogeneously from the beginning without any preprecipitation stage and coherency between the precipitate and the matrix is maintained even in an alloy aged at relatively higher temperature for prolonged periods of time.