With three Earth Explorer satellites set to launch this year, another three under construction and up to three more about to be selected for feasibility study, 2009 promises to be a significant year for ESA's contribution to Earth science - paving the way to a clearer understanding of how our planet works. Understanding how the Earth works and the way in which natural processes respond to global climate change is a major challenge facing science today. Encompassing a new approach to observing the Earth from space, ESA's Earth Explorer missions are developed in direct response to a range of Earth-science challenges identified by the scientific community.