States have often been theorized to act as competitors in crafting their environmental policies, engaging in either a “race to the bottom” or a “race to the top.” In the recent development of climate law, however, it is state collaboration and cooperation rather than state competition that have emerged most strongly. This Article first discusses how the theories of competitive state behavior would have predicted states to behave in the absence of federal action and describes the contrasting extent to which states have engaged in collaborative initiatives. The Article then analyzes why states have been motivated to collaborate in climate law