We review defect studies in as-grown and processed silicon wafers performed by the authors. These have resulted in improved understanding of substrate-related defect formation, from nucleation during the pulling process through to evolution during subsequent device processing. We summarize our results on the impact of crystal pulling conditions on grown-in oxide precipitate nuclei size/density distributions, and on the transformation of D-defects into oxide particles during high-temperature anneals. Finally, the effects of vacancy and oxygen outdiffusion on denuded zone formation and on the grown-in precipitate nuclei in the near-surface region of silicon wafers are compared. On several occasions, we also illustrate how the improved understanding of defect nucleation and transformation can be used to improve wafer quality and device yield.