This article quantifies the comparative performance of China in several dimensions. Firstly, it shows that China's move from a command to a market economy was less abrupt and more successful than that of 29 other economies making a similar transition. Secondly, while official estimates show annual GDP growth of 9.6 percent in 1978-2003, this is reduced to 7.9 percent after adjustment for exaggeration of industrial performance and growth in non-material services. Thirdly, as the exchange rate understates China's achievement, a purchasing power parity (PPP) converter is necessary to measure comparative level of performance. Our PPP converter shows that China in 2005 was the world's second largest economy, with a GDP about 80 percent of the U.S. It is assumed that China will have overtaken the U.S. as the world's biggest economy before 2015. Until recently, the World Bank estimate of the PPP for China was close to that of Maddison, but the Bank's new estimate for 2005 shows Chinese GDP about half this level. The Bank's new estimates for China and other Asian countries are not plausible, and this paper advances several reasons for rejecting them. Finally, energy use per head of population is a good deal smaller than that of the U.S., and its total energy use for a much bigger population is likely to be somewhat smaller than that of the U.S. in 2030. However, heavy dependence on dirty coal means that it will have bigger carbon emissions than the U.S. This is a major problem as Beijing and other big cities already have severe pollution problems.