Abstract: Project planning on federal public lands in the United States requires environmental impact assessment under the National Environmental Policy Act. A core component of these assessments is cumulative effects, which are the potential environmental effects of the proposed action in combination with other past, present, and reasonably foreseeable future actions on the landscape. Despite substantial case law, scientific literature, and policy about cumulative effects, analyses have remained persistently challenging and contentious. We partnered with the Bureau of Land Management (BLM) to characterize current practice of cumulative effects analysis in the agency, with the broader goal of informing development of a step-by-step cumulative effects analysis process. We developed a set of qualitative coding questions to assess cumulative effects analyses in BLM environmental assessments (EAs) against policy requirements and additional criteria regarding documentation of data, science, and analytical methods. We assessed 593 individual resource analyses in 80 EAs prepared by BLM offices in Alaska and Colorado. Alaska’s largely undeveloped landscape contrasts with the higher-activity public lands of Colorado, providing an opportunity to compare cumulative effects analyses across BLM-managed lands. We found that characteristics of analyses were similar in Alaska and Colorado. Across both states, while most (73%) analyses considered cumulative effects, few included analytical details such as specifying the geographic and temporal scope of the analysis (26% and 13%, respectively) or citing supporting literature (9%). Analyses infrequently quantified potential cumulative effects (8%). The most comprehensive analyses in our sample all focused on the cumulative effects of oil and gas development on air quality and climate change in Colorado. These findings provide insights into the kind of action-specific data, science, and methods needed to help decision makers understand how individual proposed projects may lead to cumulative effects to resources and ecosystems.