The latest move in the environmentalists’ fight against climate change involves judicial proceedings against states. In these proceedings, climate action groups seek court orders to force governments to impose more stringent measures to reduce greenhouse gas emissions. A recent judgment by a Dutch court has given this strategy momentum. In the Urgenda case, the court ruled that the Dutch government owes a duty of care to its citizens to provide protection against the risks posed by climate change. On this basis, the court ordered the government to revise its current policies to ensure that by 2020 carbon dioxide emissions are reduced by at least 25% compared to 1990 levels. As this article demonstrates, this kind of litigation raises constitutional issues, because courts may not infringe on the legislature’s prerogatives. Climate policy-making requires a series of value judgments and policy choices, and the state has non-justiciable discretion as to how it meets its duties of care.