We present first-principle total-energy calculations that clarify stable structures of B and mechanisms of B diffusion in SiO2. We find that a B atom takes a variety of stable and metastable geometries depending on its charge state. We also find that atomic rearrangements during the diffusion manifest a wealth of bonding feasibility in SiO2 and that the calculated activation energy agrees with the experimental data available. (C) 2003 Elsevier Science B.V. All rights reserved.