SMEs make up the majority of companies and employ the largest number of workers in the manufacturing and services sector and can benefit from e-commerce. However, the adoption rate of electronic commerce by SMEs is low compared to the adoption of electronic commerce by large companies. The objective of this study is to determine the critical factors that condition the adoption of electronic commerce by reviewing the literature. The results show that there are organizational, individual, technological and environmental factors. Among the factors that are frequently mentioned in the studies are external pressure, perceived utility, Perceived ease-of-use, the preparation of the organization, and the experience, knowledge and skills in Information and Communication and Technology (ICT) of the staff.