Cumulative impact analysis is examined from a conceptual decisionmaking perspective, focusing on its implicit and explicit purposes as suggested within the policy and procedures for environmental impact analysis of the National Environmental Policy Act of 1969 (NEPA) and its implementing regulations. In the paper it is also linked to different evaluation and ecisionmaking conventions, contrasting a regulatory context with a comprehensive planning framework. Finally, the specific problems that make the application of cumulative impact analysis a virtually intractable evaluation requirement are discussed in connection with the regulation of wetlands uses through the Corps of Engineers' permit program, in conjunction with the Environmental Protection Agency's responsibilities in managing its share of the 'Section 404' regulatory program requirements. To understand the purposes of cumulative impact analysis (CIA), a key distinction must be made between the implied comprehensive and multiobjective evaluation purposes of CIA, promoted through the principles and policies contained in NEPA, and the more commonly conducted and limited assessment of cumulative ecological effects (ACE), which focuses almost entirely on the ecological effects of human actions. A heuristic model that incorporates the basic elements of CIA is developed, including the idea of trade-offs among social, economic, and environmental protection goals carried out within the context of environmental carry capacity. (Copyright (c) 1988 Springer-Verlag New York Inc.)