The adoption of e-commerce by SMEs in Vietnam will enable these companies to do business in a much more efficient way. E-commerce will make these enterprises, as well as their products and services, better known, while at the same time making it possible for them to conduct transactions not only in that country, but throughout the world. The sample for this study consisted of 300 small and medium-sized enterprises in Vietnam. The results indicate that the size of the enterprise, its resources and its strategic orientation, the employees’ knowledge of e-commerce, the attitudes of managers towards innovation and their knowledge of the new technologies and of e-commerce, the intensity of the competition, the degree of support of the government, the national infrastructure, the perceived relative advantages, and the complexity and compatibility of e-commerce all have an influence on the adoption of e-commerce in SMEs in Vietnam, but that this influence differs depending on whether it involves users or prospectors.