Editors' Summary: ESA § 10(j), the Act's experimental population provision, allows the U.S. Fish and Wildlife Service (FWS) to release populations of threatened and endangered species into their historic range without complying with many of the Act's restrictions. This Article examines the statutory, regulatory, and judicial aspects of the experimental population program. It begins by examining the background for Congress' enactment of § 10(j). It then analyzes § 10(j) and the regulations that the FWS issued for implementing § 10(j). It discusses the process for issuing special experimental population rules for particular species and examines each of the special rules that the FWS has issued for experimental populations. The Article next addresses the litigation that has arisen over the Yellowstone National Park and central Idaho gray wolf experimental populations and the litigation that is expected over the Mexican wolf population. Finally, the Article analyzes the consequences of designating experimental populations and suggests species that may be next in line for designation.