The spectre of climate change is motivating businesses to evaluate the weather sensitivity of their operations and earnings. Persistent changes in day-to-day weather, such as a warmer than average winter, may prove very costly for businesses and since 1997 a new financial market has grown up around the mitigation of these day-to-day weather risks. This weather derivatives market has expanded from being a small US energy product to become a $45.2 billion industry by 2006. In the process this commodification of weather indexes is re-valuing meteorological data, forecasts and expertise, as well as changing the ways in which firms have traditionally considered weather as unmanageable. This thesis presents an empirical examination of the weather derivatives market, particularly focusing upon the UK, drawing upon in-depth interviews with market participants. Setting this within the context of current theories in human geography and science studies, the research also illustrates the material and discursive implications weather derivatives are having not just on firms and meteorology, but also climate change policies.