	Introduction

One of Justice Stevens's most lasting jurisprudential legacies is his opinion in Chevron v. Natural Resources Defense Council . The 1984 case, a landmark decision in both administrative law and separation of powers, established the legal framework that has largely governed the degree of deference a court will accord a federal agency in interpreting and implementing statutes. What began as an unexceptional case focusing on the meaning of the phrase "stationary source" in the Clean Air Act has developed into one of the most frequently cited cases ever. Although often relied on as an authority, the case has also engendered significant confusion. Questions of when, and how, to apply the two-step Chevron analysis laid out by Justice Stevens, which is simple in theory yet remarkably varied in its application, have consistently challenged federal judges. Moreover, although Justice Stevens has spent the last quarter century working to clarify the Chevron doctrine, as he departs the Court he may find himself outside the majority position on at least one key aspect of the test's application. Stevens's Chevron analysis established what many commentators have considered to be a highly deferential judicial role when faced with a challenge to an agency's interpretation of its own authorizing statute or a statute it administers. At step one, a reviewing court must determine whether Congress has spoken clearly on the issue at hand and give effect to any intent it finds Congress expressed unambiguously. An agency interpretation that is contrary to the clear intent of Congress must be rejected. If, however, Congress's intent is unclear as to the immediate question, including where Congress is silent, at step two the court's role is to defer to any reasonable agency interpretation of the pertinent statutory language. This analysis is commonly referred to as the Chevron "two-step." Inconsistent Application and Unresolved Questions

As much as Justice Stevens's opinion has been cited, major questions remain about when and how to properly apply the Chevron test. The threshold question of what agency interpretations qualify for Chevron deference, for example, remains unclear. A second ongoing dispute, and one in which Justice Stevens has played a leading role, relates to what tools of statutory construction are properly employed at step one of the test as a court determines Congress's "intent." Specifically, should the court be considering legislative intent and legislative purpose or restrict itself to the statutory language alone?
One of Justice John Paul Stevens's most lasting jurisprudential legacies is his opinion in Chevron v. Natural Resources Defense Council. The 1984 case, a landmark decision in both administrative law and separation of powers, established the legal framework that has largely governed the degree of deference a court will accord a federal agency in interpreting and implementing statutes. What began as an unexceptional case focusing on the meaning of the phrase "stationary source" in the Clean Air Act has developed into one of the most frequently cited cases ever. Although often relied on as an authority, the case has also engendered significant confusion. Questions of when, and how, to apply the two-step Chevron analysis laid out by Justice Stevens, which is simple in theory yet remarkably varied in its application, have consistently challenged federal judges. Moreover, although Justice Stevens has spent the last quarter century working to clarify the Chevron doctrine, as he departs the Court he may find himself outside the majority position on at least one key aspect of the test's application.
Stevens's Chevron analysis established what many commentators have considered to be a highly deferential judicial role when faced with a challenge to an agency's interpretation of its own authorizing statute or a statute it administers. At step one of the analysis, a reviewing court must determine whether Congress has spoken clearly on the issue at hand and give effect to any intent it finds Congress expressed unambiguously. An agency interpretation that is contrary to the clear intent of Congress must be rejected. If, however, Congress's intent is unclear as to the immediate question, including where Congress is silent, at step two the court's role is to defer to any reasonable agency interpretation of the pertinent statutory language. This analysis is commonly referred to as the Chevron "two-step."
As much as Justice Stevens's opinion has been cited, major questions remain about when and how to properly apply the Chevron test. The threshold question of what types of agency interpretations qualify for Chevron deference, for example, has narrowed. A second ongoing dispute, and one in which Justice Stevens has played a leading role, relates to what tools of statutory construction are properly employed at step one of the test as a court determines Congress's "intent." Specifically, should the court be considering legislative intent and legislative purpose or restrict itself to the statutory language alone?