Populations and economies are both growing, but at different rates. When will India overtake China to become the world’s most populous country? When will China overtake the United States to become the world’s largest national economy? This sobering, usefully quantitative book provides reasonable, if necessarily speculative, answers. In a bit of futurology, the authors imagine the world in 2050, when today’s rich countries, especially European nations and Japan, have receded in relative importance, and today’s emerging markets have become more powerful -- all while the world’s population has continued to grow, resulting in increased demand for food, energy, water, and much else. The increased pressures on the world’s resources and environment will require new and deeper forms of international cooperation. But the list of countries whose cooperation will be essential for effective results will be substantially different from the list of today’s great powers.