With alarming threats to social justice, democratic processes, and basic environmental protections looming almost everywhere we look, the question of why only some people act to improve their circumstances and the world they live in is especially pertinent today. As an environmental anthropologist, the author spent recent decades exploring how and why grassroots activists challenge extractive industrial development and devastation, but this query has relevance far beyond the author's own research specialty. With the ultimate aim of identifying common elements and areas where anthropological intervention could promote participation in campaigns for positive change, this chapter considers why activists act. Elevating the anthropology of activism to anthropology as activism expedites the essential task of increasing the number of people committed to building a better world; understanding why activists act opens new opportunities to use anthropology to do good. Perhaps most importantly, visionaries and activists (including anthropologists) can come together to convince diverse audiences that change is possible.