For the past 40 years, one of the most important doctrines underpinning administrative law in the United States was the doctrine of Chevron deference. As established in its namesake case, the Chevron deference required courts to defer to a federal agency's reasonable interpretation of a statutory provision when the agency was exercising its rulemaking authority rather than substituting the court's own interpretation when Congress' intent on the subject was ambiguous. Chevron U.S.A. v. Natural Resources Defense Council, Inc., 467 U.S. 837, 842-44 (1984).