In this study, we investigated design processes in teacher collectives, which have been made possible by new "digital" opportunities: platforms, discussion lists, etc. The object of our study is the French Sésamath teacher association and its design of a grade 10 e-textbook, more precisely the design of the "functions" chapter. We analysed it with two theoretical lenses: the documentational approach and cultural-historical activity theory. We studied the activity system of a community of teachers designing an e-textbook. At macro-level, we observed a change of objects of the activities: from designing a "toolkit" for mathematics teachers; to interactive exercises; and finally to a more "classical e-textbook". At micro-level, we analysed the development of collective documents by the community, combining resources and schemes.