What landmark case established the qualified immunity defense?

The case that established the qualified immunity defense is Harlow v. Fitzgerald. This landmark ruling clarified that government officials, including law enforcement officers, could be shielded from liability for civil damages if their conduct did not violate clearly established statutory or constitutional rights that a reasonable person would have known. The decision emphasized the need for a balance between the protection of individuals' rights and the need for officials to perform their duties without the constant threat of litigation for actions taken in the course of their duties.

By setting the standard of "clearly established law," the ruling in Harlow v. Fitzgerald established criteria that would guide the application of qualified immunity in future cases. This case is particularly significant in the context of law enforcement and correctional officers, as it firmly established the parameters within which they could operate without fear of personal liability, fostering an environment that allows officials to perform their responsibilities effectively while limiting frivolous lawsuits.