Out-of-school science learning environments enrich classroom education in many countries around the world. Numerous studies have been conducted on the effects of such learning environments, particularly their ability to promote interest. As different theories of interest were used in these studies, so far, no overview of this field of research exists. Therefore, based on a comprehensive and systematic international literature review, this article presents a detailed analysis of the theories of interest used to study out-of-school learning environments. In addition, inferences regarding situational and individual interest promotion in out-of-school science learning environments are derived, clearly showing that situational interest is promoted through these learning environments. Considering the influencing factors given in the different theories of interest, a model of student interest for these learning environments is then presented. This model can be used to guide the development and further improvement of out-of-school learning environments.