While incarcerated at the Montana State Prison, P served as an 'inmate law clerk,' providing legal assistance to fellow prisoners. P decided to assist another inmate, Tracy, with his defense against assaulting a guard. Prison rules prohibited P's assignment to the case. After discovering that other inmates had complained about Officer Galle's conduct, P sent Tracy a letter. P's letter gave Tracy hope to discover substantial evidence about Galle's conduct and encouraged Tracy to have his lawyer contact P and to not plea bargain. P's letter stated he was going to get others to start filing suits as well. D intercepted the letter. D cited P for insolence, interference with due process hearings, and conduct that disrupts or interferes with the security and orderly operation of the institution. D was found guilty of violating the first two prohibitions. The hearings officer sanctioned him by imposing a suspended sentence of 10 days' detention and issuing demerits that could affect his custody level. P then brought this action, seeking declaratory and injunctive relief under Rev. Stat. §1979, 42 U. S. C. §1983. The case was styled as a class action, brought on behalf of himself, other inmate law clerks, and other prisoners. The complaint alleged that the discipline violated due process, the rights of inmates to access the courts, and, as relevant here, P's First Amendment rights, including the right to provide legal assistance to other inmates. The District Court granted D's motion for summary judgment on all of P's claims. P was not formally acting as an inmate law clerk when he wrote the letter, and that P's claims should therefore 'be analyzed without consideration of any privilege that law clerk status might provide.' The court applied Turner and found a 'valid, rational connection between the prison inmate correspondence policy and the objectives of prison order, security, and inmate rehabilitation.' The Ninth Circuit reversed. Inmates have a First Amendment right to assist other inmates with their legal claims. This First Amendment right affected the balance of the prisoner's interests against the government's interests. The Court of Appeals upheld P's First Amendment claim. D appealed. The Supreme Court granted certiorari.