This paper explores the prospects for a global carbon market as the centrepiece of any serious attempt to reach the ambitious goal for greenhouse gas (GHG) reductions set by climate scientists. My aim is to clarify the extent to which we know what policy might best support global decarbonisation. We begin by discussing what we might mean by a global carbon market and its theoretical properties. We then go on to discuss the EU Emissions Trading System experience and the recent experience with the Australian carbon tax. Next, we assess recent carbon market initiatives in the US and in China. My argument is that while establishing the amount of emissions required and dividing it up acceptably between countries requires an enormous scientific and international negotiations effort, the economic instruments to deliver the agreed targets are readily at hand.