The Bureau of Land Management (BLM) (defendant) created the Cooperative Management Agreement (CMA) program, allowing ranchers to manage livestock grazing. The CMA program was established by a regulation (CMA regulation) that authorized the BLM to enter into special permit arrangements with ranchers who demonstrated “exemplary rangeland management practices,” a term not defined by the regulations. BLM officials had the discretion to determine which ranchers could participate in the CMA program. The CMA regulation (1) bound the BLM to the program terms for 10 years, (2) authorized permit evaluations no earlier than every five years, (3) allowed permit cancellation or modification only in limited circumstances, (4) automatically renewed permits if the agreement’s objectives were being met, and (5) gave permittees 10 years to comply with agreement objectives that were not being met. The Natural Resources Defense Council and others (plaintiffs) challenged the BLM’s CMA regulation on the basis that the regulation violated the duties of the secretary of the interior (secretary) (defendant) under the Taylor Grazing Act (Act), 43 U.S.C. §§ 315 et seq.; the Federal Land Policy and Management Act (FLPMA), 43 U.S.C. §§ 1701 et seq.; and the Public Rangelands Improvement Management Act (PRIA), 43 U.S.C. §§ 1901 et seq. The plaintiffs moved for summary judgment. The defendants also moved for summary judgment, arguing that the CMA regulation was valid because it required the specification of performance standards.