Awareness of environmental problems has increased dramatically over recent decades, but individual action to address environmental issues has remained stagnant. Shifting social identities may be an under-appreciated explanation of this gap: identification with environmentalists in the U.S. dropped from 78% to 42% since 1991. In four pre-registered studies of U.S. residents (total N = 2,033), we explored the predictors and outcomes of environmentalist identity. We also developed a novel implicit measure of less deliberate aspects of environmentalist identity. We used explicit and implicit environmentalist identity to predict self-reported environmental behaviors and policy preferences. Meta-analysis of our studies revealed that explicit identity was moderately associated with implicit identity (r = .24). Explicit identity strongly and uniquely predicted pro-environmental behaviors and policy preferences (partial rs = .58, .62), while implicit identity did not uniquely predict either (partial rs = .05, .05). Our findings highlight the importance of social identity in conservation.