Kisor (P), a Vietnam War veteran, sought disability benefits from the Department of Veterans Affairs (VA) in 1982, alleging that he had developed post-traumatic stress disorder from his military service. His initial request was denied, but in 2006, P moved to reopen his claim. The VA this time agreed he was eligible for benefits, but it granted those benefits only from the date of his motion to reopen, not from the date of his first application. Under the VA’s regulation, the agency could grant P retroactive benefits if it found there were “relevant official service department records” that it had not considered in its initial denial. P had come up with two new service records, both confirming his participation in Operation Harvest Moon. The Board held those records were not “relevant” because they did not go to the reason for the denial-that P did not have PTSD. The Board of Veterans’ Appeals affirmed that retroactivity decision, based on its interpretation of an agency rule governing such claims. The Court of Appeals for Veterans Claims affirmed. The Court of Appeals for the Federal Circuit also affirmed, but it did so based on deference to the Board’s interpretation of the VA rule. The Court of Appeals for the Federal Circuit also affirmed, finding the regulation “ambiguous” as between the two readings. (one reading was the records had to relate to the present disability claim and the other was the records could be a new basis for disability). The court believed Auer deference appropriate: The agency’s construction of its own regulation would govern unless “plainly erroneous or inconsistent with the VA’s regulatory framework.” The Supreme Court granted certiorari.