Eco-anxiety and climate anxiety are widely discussed in contemporary media and are subjects of growing research interest. However, there is a lack of research about the definitions and variations of these phenomena. This article analyzes various views of eco-anxiety from a wide range of disciplines. Insights from various anxiety theories are used to discuss empirical studies about forms of eco-anxiety. The article points out that uncertainty, unpredictability, and uncontrollability seem to be important factors in eco-anxiety. Most forms of eco-anxiety appear to be non-clinical, but cases of “pathological” eco-anxiety are also discussed. Other relevant terms and phenomena are scrutinized, such as ecological grief, solastalgia, and ecological trauma. The relationship between studies on eco-anxiety and research about ecological emotions and affect is probed. Eco-anxiety is found to be closely connected to fear and worry, but several disciplines include discussion of its character as existential anxiety. Psychosocial and sociological perspectives point out that social dynamics shape forms of eco-anxiety in profound ways. While paralyzing forms of eco-anxiety emerge as a problem, it is noted that eco-anxiety manifests itself also as “practical anxiety”, which leads to gathering of new information and reassessment of behavior options. This variety of forms of eco-anxiety should be taken into account in healthcare and public discussion.