During her visit to the United States to promote her book The Challenge for Africa, Lantern author and Nobel Peace Prize Laureate Wangari Maathai spent a few days in Calistoga, California, where Lantern had the good fortune to catch up with her. In this video, made in collaboration with The Green Belt Movement, Prof. Maathai talks about the Billion Tree Campaign campaign, which has so far planted over a billion trees, had two billion more pledged, and aims to plant seven billion in total by December 2009.