A more thorough explanation:

Definition: Sovereign immunity is the principle that the government cannot be sued without its consent.

Overview: Sovereign immunity comes from British common law and means that the King could do no wrong. In the United States, sovereign immunity usually applies to the federal and state governments, but not to municipalities. However, the federal and state governments can choose to waive their sovereign immunity. For example, the Federal Tort Claims Act waives federal immunity for certain types of tort claims.

Examples: If a person is injured during their military service, they cannot sue the federal government because of the Feres Doctrine. Also, federal employees cannot be sued for torts committed during the scope of their employment because of the Westfall Act.

Citizens Suing Their Own State: When a citizen wants to sue a state actor (someone acting on behalf of the state), courts will typically use one of four tests to determine if the actor is subject to liability:

1. Governmental v proprietary function test: If the actor was performing a proprietary function, then they are subject to liability. If the actor was performing a governmental function, then they are not subject to liability.
2. Ministerial/operational v. discretionary functions/acts test: If the actor is performing a ministerial/operational action, then there is no immunity. If the actor is performing a discretionary action, then there is immunity.
3. Planning v implementational: If the actor's planning of policy results in harm, then there is immunity. If the harm happens due to the government's implementation of the plan, then there is not immunity.
4. Non-justiciable v. justiciable: If the action is justiciable under regular tort principles, then there is no immunity. If the issue is not justiciable under regular tort principles, then there is immunity.

Citizens Suing Other States: In the past, a citizen of one state could sue another state. However, the Eleventh Amendment now prevents this from happening.

Explanation: Sovereign immunity means that the government cannot be sued without its consent. This applies to both federal and state governments, but not to municipalities. However, the government can choose to waive its immunity. There are different tests to determine if a citizen can sue a state actor, and the Eleventh Amendment prevents citizens of one state from suing another state.