Despite recent studies on determinants of adoption and diffusion of e-procurement, the existing literature is still scant on how different variables affect eprocurement adoption, diffusion and upscaling by type of adopter. Using qualitative data from interviews, this paper aims at contributing to fill this gap by examining how outer and inner variables influence the adoption and upscaling of e-procurement in two European regions that can be considered as innovators (Valencia in Spain and Lombardy in Italy). Our findings show that 1) the role of inner factors is clearer than that of outer ones in adoption processes, 2) in particular, organizational (mainly slack resources in both cases) and individual determinants seem to be the most important inner factors, 3) change management strategies and activities have a key role in upscaling processes, and 4) the internal organizational context and the type of technological innovation may act as moderators/mediators of the effects.