This article is a commentary on the mathematical working space (MWS) approach and draws on the articles contained in this "ZDM" issue. The article is divided into three parts. In the first part I discuss the place of the MWS approach among the French theories of didactique des mathématiques. In the second part I outline what I think are the central ideas of the MWS approach. I conclude the article with a sketch of what seems to me to be its accomplishments and challenges, focusing mainly on the epistemological and cognitive stances that the MWS approach conveys in order to elucidate the manner in which this approach theoretically assumes that things are known and learned.