Density functional theory calculations were used to explore the mechanism of Me3PAuOTf (gold)- and TfOH (Brnsted acid)-catalyzed nucleophilic additions to olefins. Addition of N- and O-nucleophiles have been theoretically modeled by the reactions of CbzNH2 (hydroamination) and PhOH (hydroalkoxylation) with ethene. Both gold(I) and Brnsted acids are shown to be active catalysts for the reaction. The gold-catalyzed mechanisms were found to be fully consistent with those proposed earlier for the hydroamination of dienes and hydroalkoxylation of alkenes. The gold(I)-catalyzed hydroamination was found to be stepwise, whereas the hydroalkoxylation was found to proceed via a concerted step. The TfOH-catalyzed process was found to be concerted. © 2010 American Chemical Society.