In their contribution, Marcos Felipe-Rodriguez, Gisela Böhm and Rouven Doran analyze from an environmental psychological perspective which factors contribute to a risk perception of microplastics. While only few studies on risk perception of microplastics exist, they discuss different heuristics and concepts with respect to the topic of microplastics. Drawing on the psychometric paradigm (Fischhoff et al. 1979), they analyze the main risk perception features of microplastics that show characteristics of an “unknown risk”, since it is a rather new risk and not easy to observe including its potential delayed effects. Furthermore, they discuss how specific perceiver characteristics, such as socio-demographics, reasoning knowledge and fairness, as well as values and worldviews impact risk perception. Another important factor are emotions, that are grouped according to consequentialist and moral emotions. Microplastics activate both forms of emotions. While consequential emotions comprise fear, for example about consequences of microplastics for sea animals, moral emotions on the other hand are linked to outrage and guilt over violating moral norms, such as the plastic pollution of environments caused by humans. Next to emotions, mental models, that is how people mentally conceive microplastics regarding their causes, consequences, and solutions, are also crucial for risk perception research on microplastics.