Tony Lelièvre (CERMICS) and David Picard (IMAGINE) have been invited to coordinate the third volume of the journal “Transitions” on “Models and data for the environment”. This volume includes many contributions from researchers working at CERMICS and IMAGINE, and more generally from scientists and engineers who use numerical methods in their everyday life to nourish their research on the ecological transition. The articles will be presented and discussed on the 26th October (see the program and the flyer), with in particular three round-tables with the authors on the three main subjects addressed in this volume: transport and mobility, climate, and energy.