Teaching as productive activity in society is labour (Arbeit; travail). We will take the classical definition by Marx as starting point: “In the labour-process, therefore, man’s activity, with the help of the instruments of labour, effects an alteration, designed from the commencement, in the material worked upon.” (1887, p. 94). If teaching is labour, one has to ask what are its instruments and what is the material worked upon. We will propose an answer to this question based on Vygotsky’s theory that uses Marx’s definition of labour. Our thesis: the teacher’s instruments are semiotic. Teaching can be defined as a double semiotic process: on the one hand, the objects themselves that have to be taught and learned are socio-historical products, “oeuvres”, in a very large sense, products of human labour; on the other hand, didactic instruments allow to point to certain aspects of the oeuvres. These latter instruments are clearly epistemic, related to knowledge. Teaching is therefore necessarily an epistemic practice that can relate to contents that also are epistemic. We will illustrate teaching as double “semiotisation” through the analysis of videotaped practices of teaching grammar, text writing and literature.