The Fifth Edition is updated to take account of new developments in the law, new regulations, and new cases, as well as the multiple and ongoing regulatory changes and reversals among the Obama, Trump, and Biden Administrations. In addition, the casebook has been modified throughout to call more attention to environmental justice issues. Chapter 1 (RCRA and CERCLA) and Chapter 4 (Clean Air Act) now have expanded discussions of how environmental justice issues arise in the context of pollution control permitting. Chapter 2 (NEPA) includes two of the Standing Rock Sioux decisions about the Dakota Access Pipeline. In addition, the Introduction chapter has been revamped to more thoroughly introduce non-statutory approaches to environmental law, including constitutional and common-law approaches to the public trust doctrine and a brand new section on the Rights of Nature movement, emphasizing the environmental justice and indigenous rights tie-ins to those movements, before shifting to a discussion of why states and the federal government would choose statutes, a theme continued at the beginning of Chapter 1. The challenge of the Fifth Edition is the ongoing changes to environmental regulations in the opening year of the Biden Administration. The Fifth Edition updates through June 2021 and points to resources for keeping track of new developments. It discusses continuing regulatory issues such as climate change under the Clean Air Act and "waters of the United States" under the Clean Water Act in some detail, emphasizing the issues in contention and explaining why the EPA's regulatory approach continues to evolve.