This dissertation investigates the U.S. Forest Service's (USFS) implementation of the cumulative effects analysis (CEA) requirement under the National Environmental Policy Act (NEPA). The CEA regulation requires federal agencies to provide an analysis of environmental effects, with consideration of past, present, and foreseeable future actions by both public and private parties, often on broad geographic scales. Studies in the late 1990's found that compliance with CEA requirement was highly variable across agencies. Of late, judicial enforcement of the CEA requirement has been on the rise with the USFS the focal agency in the majority of decisions. This study investigates USFS implementation of the CEA requirement, with a focus on wildlife, and uses the Idaho Panhandle National Forest (IPNF) as a case study. Case law and NEPA document analysis, along with semi-structured interviews, are used to investigate: legal standards for CEA and wildlife analysis, the current state of CEA practice, impediments to implementation, and opportunities for improvement. The case law analysis reveals that plaintiffs have successfully challenged the agency for failure to consider other relevant projects in a CEA, lack of rationale for findings, reliance on stale data, and failure to include CEA at the appropriate junctures in the planning process. Findings from the IPNF case study indicate that landscape-level analysis and the inclusion of past actions in CEA continue to be major challenges in implementing the requirement. Confusion over the nature of the requirement, limited monitoring data, and lack of time and funding impede the agency's ability to effectively conduct CEA. Cumulative impacts to wildlife are measured in terms of changes to suitable habitat. No clear picture is provided of changes to habitat availability or population status over time. The efficacy of using habitat as a proxy for species presence is questionable, as is the scientific foundation of some tools used by the IPNF to support its wildlife CEA. Recommendations, such as improved monitoring, better understanding of species-habitat relationships, and options for increasing the scientific credibility of agency decisions, are discussed herein as ways to improve wildlife planning and CEA on USFS lands.