The O-C bond dissociation energy (Delta H(r)degrees(T)) in alkoxyamines appears to play a key role in the nitroxide-mediated living free radical polymerizations, and an efficient control of the process can be achieved for Delta H(r)degrees(T) between 20 and 30 kcal/mol. We report in this paper density functional theory calculations of the O-H and O-C bond dissociation energies of different hydroxylamines and alkoxyamines. Optimization procedures, basis set effects, and exchange-correlation functionals are compared and tested against experimental data. Finally, the bond dissociation energy of (N-tert-butyl-1-diethylphosphono-2,2-dimethylpropylnitroxide)R " (where R " = benzyl, styryl), is reported. This last result is especially important since SG1 is the most efficient to-date nitroxide radical in nitroxide-mediated polymerizations of styrene and acrylates.