Scientists know that the environmental effects of separate projects can accumulate to pose significant risks. Yet law often allows unintended environmental harms by ignoring cumulative effects, or using weak controls that fail to prevent harm in practice. This innovative research aims to analyse and evaluate the theoretical bases, adoption and use of laws regulating cumulative environmental effects in the US, EU, Canada and Australia. Using novel methods combining law, ethics, and natural and spatial science, this project seeks to build an framework of globally relevant best practice tools for regulating cumulative effects. This promises to increase the capacity of regulators, industry, and the community to better manage environmental harms.