This article examines science teaching and learning by drawing on Vygotsky's sociocultural theory of learning and development as well as a social semiotic perspective. The latter perspective includes in semiosis the science equipment, science phenomena, teacher and student actions, talk and writing that are involved in science teaching and learning. In much the same way a Vygotskian perspective views science phenomena and equipment as technical tools that mediate both teacher and student meaning making, as do the symbolic products created by the teacher and the students. We suggest an inclusive view in which all are seen as active mediators in science teaching and learning.