Climate change may bring about anxiety, which may be referred to as eco-anxiety. Commonly accepted conceptual or diagnostic criteria for eco-anxiety are currently lacking. Here, we briefly summarize the current literature on climate change and mental illness. We suggest dividing the concept of eco-anxiety into adaptive eco-anxiety and an anxiety disorder where climate change plays a major role. This distinction may be helpful in clinical practice to discern relatively common and potentially healthy eco-anxiety from a disorder causing impairment in daily functioning. Benefits of adaptive eco-anxiety include the development of active coping strategies (increasing resilience) as well as behavioural changes to mitigate climate change. When debilitating anxiety comes with avoidance and centers around climate change, a specific phobia called eco-anxiety disorder may be considered. Importantly, as validated diagnostic criteria for this disorder are currently lacking, further conceptualization is highly needed. Future clinical research may help fill these current knowledge gaps.