This article presents a research program in education, which is developed within an enactive perspective and focuses on human activity. More speciically, activ- ity is conceptualized as dynamic, meaningful for the actor, giving rise to experience and autonomous. he analysis of actual activity in working and training situations high- lights phenomena of simplexity, which are summarized in three points: transparency and appropriation, mimesis, and typicalisation. As a conclusion, the article points out some avenues taking seriously these phenomena of simplexity for designing professional learning environments.