How can we reasonably justify a climate policy goal if we accept that only possible consequences from climate change are known? Precautionary principles seem to offer promising guidelines for reasoning in such epistemic situations. This chapter presents two versions of the precautionary principle (PP) and defends one of them as morally justifiable. However, it argues that current versions of the PP do not allow discrimination between relevant climate change policies. Therefore, the chapter develops a further version of the PP, the Controllability Precautionary Principle (CPP), and defends its moral plausibility. The CPP incorporates the following idea: in a situation when the possible outcomes of the available actions cannot be ranked with regard to their value, the choice between available options for action should rest on the comparison of how well decision makers can control the processes of the implementation of the available strategies.