The incorporation of socioscientific issues into science teaching to promote students' scientific literacy may require that science teachers reconsider and transform their teaching practices. This study examines the knowledge and considerations involved when two teachers incorporated socioscientific issues into their teaching, with the aim of understanding conditions for developing teaching to promote functional scientific literacy. Data consisted of written records of teaching, field notes of classroom observations and transcripts of meetings between the teachers and a researcher, generated during a year-long professional development project. Data were analysed through the framework of didactics that understands teaching as framed by societal conditions, curricula, teaching traditions and teacher and student knowledge and intentions. The results show that the incorporation of socioscientific issues enabled student engagement with scientific content, the practice of evidence-based reasoning and the consideration of values and norms. The teachers strove to seize upon student questions in teaching, and the results show that this may require strategies to raise questions among students, as well as profound science content knowledge on the part of teachers. Moreover, the results indicate that tensions arose between students' instrumental views of teaching and learning and the teachers' promotion of an exploratory classroom culture. The teachers had to support student adaption to the new requirements, and in this process, mutual trust and clear expectations were considered important. Implications for teachers' professional development in relation to the incorporation of socioscientific issues in science education are discussed.