A quantitative description of the transient diffusion and activation of boron during post-implantation annealing steps is one of the most challenging tasks. In industrially relevant situation, it needs to address diffusion at extrinsic concentrations, the agglomeration of self-interstitials, and the formation of boron-interstitial clusters. This article describes the experimental work performed or used to calibrate model parameters as independently as possible. The combined model is then applied to ultra-shallow junction formation by annealing boron implanted into crystalline or preamorphized silicon.