Cumulative effects assessment (CEA) is a sub-discipline of environmental impact assessment that is concerned with appraising the collective effects of human activities and natural processes on the environment. Aspirations for CEA have been expressed by many authors since 1969, when the foundation of environmental appraisal was laid by the US National Environmental Policy Act. This paper's purposes are (i) to review aspirations for CEA, relative to current practice; and (ii) to fully explain and critique the logic that connects CEA's operational steps and underlying philosophies. A literature review supports the following statements: Some conceptualizations emphasize the delivery of information to support decision making as the key purpose of CEA; others deem collaboration, debate, and learning as most important. Consensus on CEA's operational steps has been reached, but each step requires practitioners to make analytical decisions (e.g., about the scope of issues to include or the time horizon to consider) and objective rules for how to approach those decisions are lacking. Numerical methods for assessing cumulative effects are largely available, meaning that CEA's biggest problems are not scientific. CEA cannot succeed without substantive public engagement, monitoring, and adaptive management. CEA is best undertaken regionally, rather than project-by-project. CEA and planning are complementary, and should be merged. In its most enlightened form, CEA is a useful tool for ensuring that human undertakings ultimately conform to Earth's finite biosphere, but current practice falls short of the ideal, and CEA's logical derivation is not entirely sound. As regards CEA's big problems, sustainability has not been defined clearly enough to make criteria for judging the significance of cumulative effects indisputable; legal, regulatory, and institutional frameworks are poorly aligned for CEA; and objective criteria for judging the adequacy of CEAs scope, scale, and thresholds do not exist, which makes the question of how to provide general guidance to practitioners intractable. Recommendations call for sustainability goals to be clearly expressed as measurable targets. Furthermore, precaution in human enterprise should be exercised by avoiding, minimizing, restoring, and offsetting negative cumulative effects. CEA can assist by quantifying and optimizing trade-offs.