States enjoy immunity from suit in federal court, which shapes the structure of constitutional litigation against state government.
Scope. The immunity bars suits against a state by private parties for damages and, in many circumstances, for retrospective relief. It extends to arms of the state, determined by factors including funding responsibility, state control and the entity’s characterisation under state law. Counties and municipalities are generally not arms of the state.
Exceptions. Consent by the state; abrogation by Congress under its power to enforce the Reconstruction Amendments, subject to congruence and proportionality; and the officer suit.
The officer suit. A suit against a state official in their official capacity seeking prospective injunctive relief to end an ongoing violation of federal law is not treated as a suit against the state. The inquiry is straightforward: does the complaint allege an ongoing violation and seek relief properly characterised as prospective?
What it does not permit. Retrospective monetary relief payable from the state treasury, or claims resting on state law.
Individual capacity suits for damages against officials are unaffected by sovereign immunity, though qualified immunity applies.
Practical pleading. Constitutional challenges to state programmes are therefore framed against named officials, prospectively, with any damages claims directed at individuals personally.