The time frame of this article covers the Portuguese transition to democracy in the 1970s until the 1990s, when democratic institutions operated fully. The focus lies on the way in which changes in the conceptualization of nature and society and their mutual relationship were reflected in secondary education textbooks. We explore whether and how knowledge about both domains provided in textbooks contributed toward democratic education and toward the exercise of citizenship at a time when democracy was in the making. Both natural sciences and history textbooks express environmentalist concerns and promote an ecological perspective. History textbooks frame these concerns in the social, cultural, and political contexts of the time.