Citizen science is expected to play an important role in relation to scientific literacy Vision III for students living in the future society. This study aims to identify the characteristics of extreme citizen science (ECS) and extreme citizen scientists (ECSs) and to derive key competencies of ECS?s using literature analysis from Korean and international educational contexts. The characteristics of ECS are identified were as follows: Citizens recognize problems, set research topics, establish data collection plans to solve them, analyze and interpret collected data, and conduct social action. Three categories of key competencies for ECS?s were derived: Thinking scientifically with appropriate knowledge, exploring as knowledge producers, and acting while considering both individuals and communities. The results of this study can be used for developing citizen science competency measurement tools, development of ECS programs, and training of ECSs. Implications for future research are considered.