The notion of didactical engineering has influenced and characterized contemporary research in mathematics education in France to an important extent. In this paper, we address the following from an insider's and an outsider's perspective: (1) the way this notion is theoretically grounded, (2) the kinds of design research practices it has led to and is leading to, and (3) the way it relates to the design research paradigm. As a conclusion, we highlight similarities and differences between the two perspectives and recommend further discussions to the benefit of both didactical engineering from an insider's and an outsider's perspective.