Based on the literature on the diffusion of innovation and on information systems (IS), and building on emerging concepts in electronic commerce (e-commerce), this paper measures the influence of various factors (i.e., those that relate to the technology itself, to the present use of e-commerce and to business relationships) on firms? future level of use of electronic marketplaces (e-marketplaces). This theoretical model is tested on data collected from 1,200 senior managers in Canadian firms. Findings indicate that a firm's past experience in e-commerce and factors that relate to its business relationships ultimately affect its future use of e-marketplaces. Results of TOBIT regressions also show that the complexity of sophisticated e-commerce implementations is negatively correlated with the future level of use of e-marketplaces and that consultants and other experts play an essential role in encouraging and facilitating the use of this new type of electronic platform. Finally, our survey data demonstrate that the relative influence of some determinants differs according to the firms? size.