This chapter contains notes written from 1929 to 1931 connected with the introduction of the systemic principle into cultural–historical theory. In Vygotsky's publications, this principle was first discussed in his article "About psychological systems' (October 1930), but the present series provides the broader historical context of Vygotsky's rethinking of the concept of higher psychological function. Instead of the function, it is now the interfunctional connections that become the focus of attention.