We review the results of several experiments aimed to elucidate the thermal evolution of the self-interstitial excess introduced by Si-ion implantation in crystalline Si. Deep-level transient spectroscopy and photoluminescence measurements were used to monitor how those interstitials are stored into stable point-like defect structures just after implantation, evolve into defect clusters upon annealing at intermediate temperatures. and are annealed out, releasing the stored self-interstitials upon annealing at larger temperatures. It is shown that although dopant atoms and impurities (C and O) are not the main constituents of these clusters, the impurity content has a large effect on the early stage of cluster formation, at low fluence and low temperatures. and can affect their dissociation kinetics. A stable residual damage, electrically characterized by two signatures at E-v +0.33 eV and E-v + 0.52 eV and exhibiting two broad signatures in the photoluminescence spectrum, is present for doses greater than or equal to 10(12)/cm(2) and annealing greater than or equal to 600 degreesC. This residual damage, formed by interstitial clusters. is stable to temperatures as high as 750 degreesC and anneals out with an activation energy of similar to2.3 eV. It is suggested that these clusters store the interstitials that drive transient enhanced diffusion at low implantation doses and/or low temperatures, when no extended defects are formed. Finally. when 311 extended defects form the luminescence spectrum is dominated by a sharp signal at 1376 nm, which we correlate with optical transitions occurring at or close to these defects. Dose and temperature thresholds for the transition from small clusters to extended defects have been observed and will be discussed.