Climate change has quickly emerged as one of the hottest topics in NEPA (the National Environmental Policy Act) analysis. Analysis of climate change impacts in NEPA documents is a fairly recent development; many NEPA documents today contain no such analysis. Although a few federal agencies have addressed greenhouse gas emissions and related climate change impacts in documents for some time, such analyses have been historically atypical. The recent widespread media attention on climate change, however, coupled with a substantial increase in litigation focusing on climate change impact analysis in NEPA documents, has driven a rapid rise in interest over how to incorporate such analysis into NEPA analyses. This article is part one of a two-part series, briefly describing the context for considering climate change in NEPA analyses and reviewing the case law and other legal developments centered on NEPA climate change. Part two, to appear in a subsequent issue of Environmental Practice, will discuss methodological approaches, analysis techniques, and mitigation measures for addressing climate change in NEPA analyses.