The presentation focuses first on core concepts and constructs from the cultural historical school, in particular as presented in the works by Vygotsky and Leontiev. Selected contributions from Vygotsky and Leontiev such as mediation, tools, artefacts and activity are presented to illustrate the grounds of the research work done within TVET by scholars at Stockholm University. The work by Finnish researcher Yrjö Engeström and in specific the cycle of expansive developmental research has been used of frequent use in research in TVET at Stockholm University. A case study will be presented to illustrate how this theoretical model has been used in research. Overall the presentation intends to highlight and inspire discussion about benefits and challenges of using activity theory in research on TVET.