Constructivism has become an important referent for research and practice in science education. A variety of more or less divergent forms of constructivism have developed: discussion between these is occasionally heated. Six such forms are briefly described in order to provide an overview of the held of constructivist theory. A scheme for characterising constructivist writing on the basis of its relative emphasis on (a) personal versus social construction of knowledge and (b) objectivist versus relativist views of the nature of science is suggested. Issues of theory creation and reflexivity, central to constructivist practice, are discussed. It is suggested that debate about the “best” form of constructivism is counterproductive. A more powerful approach to epistemology is that described by Feyerabend, the holding in dialectical tension of a variety of incompatible perspectives.