Poliedra took part in the work group of consultant companies who carried out the SEA of the Expo Milano 2015 Plan, the urban planning act with a variance role, necessary to make possible the site transformation before and after the Expo event. Poliedra covered a responsibility role as regards the following themes: methodological and procedure aspects, environmental monitoring system design, environmental compensations criteria, air pollution, energy and greenhouse gas emissions. The assessment considered the whole life cycle of the event and gave criteria to minimize impacts within each phase: the building phase, the event with its management aspects, the site transformation after the event closure.