Today's enormous development challenges are complicated by the reality of climate change-the two are inextricably linked and together demand immediate attention. Climate change threatens all countries, but particularly developing ones. Understanding what climate change means for development policy is the central aim of the World Development Report 2010. Estimates are that developing countries would bear some 75 to 80 percent of the costs of anticipated damages caused by the changing climate. Developing countries simply cannot afford to ignore climate change, nor can they focus on adaptation alone. So action to reduce vulnerability and lay the groundwork for a transition to low-carbon growth paths is imperative. The 'World Development Report 2010' explores how public policy can change to better help people cope with new or worsened risks, how land and water management must adapt to better protect a threatened natural environment while feeding an expanding and more prosperous population, and how energy systems will need to be transformed. The authors examine how to integrate development realities into climate policy-in international agreements, in instruments to generate carbon finance, and in steps to promote innovation and the diffusion of new technologies. The 'World Development Report 2010' is an urgent call for action, both for developing countries who are striving to ensure policies are adapted to the realities and dangers of a hotter planet, and for high-income countries who need to undertake ambitious mitigation while supporting developing countries efforts. The authors argue that a climate-smart world is within reach if we act now to tackle the substantial inertia in the climate, in infrastructure, and in behaviors and institutions; if we act together to reconcile needed growth with prudent and affordable development choices; and if we act differently by investing in the needed energy revolution and taking the steps required to adapt to a rapidly changing planet.