As future citizens, students must make decisions requiring an understanding of the interaction of science and technology and its interface with society. STS education has been strongly identified with meeting this goal, but putting theory into practice has so far been difficult. This article asks, “What are the challenges influencing science teachers to implement STS education in the science classroom?” The author investigated using a mixed method research technique incorporating multiple sources of qualitative and quantitative data (questionnaire, interviews, field notes, (...) and classroom observations). Constraints a fecting teachers' practices in teaching science through STS education were identified and can be categorized into impersonal, interpersonal, and personal constraints. Findings indicated interactions within and between external and internal constraints. Suggestions are made for implementing change in various aspects of science teacher education. (shrink)