China constitutes a fifth of the world's population. Over the last 20 years its economy has doubled to make it the fifth largest economy in the world; if the pace is repeated over the next 20 it is set to become second only to the US. The speed of its development is stunning, a combination of cheap labour and commitment to science and technology that has never been matched by a developing country. The re-emergence of China as a superpower constitutes the biggest challenge the world has had for more than a century. Never before in modern times has the financial, trade, economic and diplomatic world pecking order been so profoundly reconstituted. This is a transition – both internally in China and externally in the world beyond – beset by hazard and risk. The world's peace and prosperity depends upon it being executed successfully.