The main purposes of this paper are to identify critical success factors (CSFs) for electronic commerce (e-commerce) in Thailand and explain the major influences behind these factors. Detailed case studies of nine e-commerce companies from different industries in Thailand were conducted. Results showed that social behavior and national culture, more specifically issues pertaining to trust and shopping behavior, were the major influences for the success of e-commerce in Thailand. The phenomenon could be partly explained by Hofstede’s cultural dimensions. Thailand’s infrastructure also played an important role in the success of its e-commerce development. The findings provide a framework to guide the development of e-commerce ventures in Thailand and other developing countries with similar cultures and infrastructures.