The weight of scientific evidence indicates that climate change is causally associated with collective violence. This evidence arises from individual studies over wide ranges of time and geographic location, and from two extensive meta-analyses. Complex pathways that underlie this association are not fully understood; however, increased ambient temperatures and extremes of rainfall, with their resultant adverse impacts on the environment and risk factors for violence, appear to play key roles. Collective violence due to climate change poses serious threats to health and human rights, including by causing morbidity and mortality directly and also indirectly by damage to the health-supporting infrastructure of society, forcing people to migrate from their homes and communities, damaging the environment, and diverting human and financial resources. This paper also briefly addresses issues for future research on the relationship between climate change and collective violence, the prevention of collective violence due to climate change, and States’ obligations to protect human rights, to prevent collective violence, and to promote and support measures to mitigate and adapt to climate change.