Preconceptions are a crucial factor in the educational learning process. Hence, the investigation of preconceptions is important for learning and teaching in the field of geography. This study examines the preconceptions of 12- and 13-year-old students, regarding the major environmental problem of "desertification." The students' preconceptions were collected by conducting half-standardized, problem-centered and guided interviews. These interviews (n = 13) were then evaluated using qualitative content analysis. Results show quite complex preconceptions concerning the causes, the processes, the effects and the measures to counter desertification. Regarding the causes of desertification, three basic preconceptions were identified: water consumption inducing drought, climate change generating high temperatures and wind blowing sand from deserts to adjacent areas. All in all, natural causes for desertification were predominant from the students' perspective. In conclusion, some conceptions can be classified as almost in line with scientific explanations, while others can be considered as alternative explanations. Based on the results of the study, implications concerning learning and teaching geography are proposed, such as focusing on the anthropogenic causes of desertification.