We conducted three independent studies to support the Spanish version of the Environmental Attitudes Inventory (EAI). The first study consisted of translating and pre-testing on a sample of 125 college students. The second consisted of testing the EAI on a sample of 225 university students in several undergraduate courses. Student data were collected using two different methods, through an online teaching platform and in the classroom. The findings were symmetrical in terms of precision and dimensionality. The third study completed the aforementioned ones testing the items on a representative sample from the general population in Spain. The participants were 630 citizens from 17 regions and responded to the EAI using an online platform. The results of the factor analysis led us to propose a measurement model, with 18 items and six first-order factors: environmental movement activism, conservation motivated by anthropocentric concern, confidence in science and technology, personal conservation behaviour, human dominance over nature, and support for population growth policies. External validity evidence was assessed by the correlation with the following variables: neuroticism, ecological behaviour, limits to economic growth, economic liberalism, sustainability, altruism, and social desirability. These estimations stayed away from demographic and personal aspects such as age, sex, political ideology, and region.