The failure of much curriculum innovation has been attributed to the neglect by innovators of teachers' perceptions. The purpose of this study was to investigate inservice science teachers views of integrating Science, Technology and Society (STS) issues into the science curriculum and identify the factors that influence their decisions concerning integrating STS issues (or not). The study used mixed methods (questionnaire and interviews) with Egyptian science teachers who teach science courses for 12- to 14-year-old students. The findings indicate that unless curriculum developers take account of teachers' beliefs and knowledge and the sociocultural factors that shape or influence those beliefs in designing and planning new STS curriculum materials, these materials are unlikely to be implemented according to their intended plan.