I briefly review the relevance of radioactive nuclei for timingevents of interest in the evolution of the Solar System. The relatedtechniques are based on nuclear radio-chronometry of terrestrial ormeteoritic samples. A special attention is paid to short lived($\bar \tau \le$ 100 Myr) isotopes produced by stellarnucleosynthesis: I mention the indirect information we have on theirpresence in the early solar nebula, and discuss their use both forestablishing very precise isochrons in the initial evolutionarystages of the Solar System, and for inferring the history ofnucleosynthesis prior to the Sun's formation. In particular, fromthe existing record of a few important nuclei (26Al, 60Fe,205Pb, 41Ca among others) it appears that the protosolarnebula was subject to late contaminations both by spallationreactions in the fast winds of the early Sun, and by a nearby star.The recent suggestions that this last was of low or intermediatemass are also discussed.