This study examines the social beliefs and values of the Spanish population with regard to environmentalism. A questionnaire on environmental beliefs was produced and administered to two sample groups. The first group, to be called “activists” (comprising 86 subjects), is characterized by belonging to one or other environmental organization. The other, termed “nonactivists” (comprising 410 subjects), is composed of people not belonging to any environmentalist organization. We conclude that, as in other Western countries, environmentalism has moved from being a set of beliefs held by a small group of people to becoming a central element in the system of beliefs characterizing our society. In other words, the beliefs of the environmentalist movement are being gradually built into a new ideology. However, we found differences between activists and nonactivists, which we interpret both in terms of Milbrath's theoretical model and as contradictions of postmodernist culture.