A legal doctrine that is used to protect state and federal officials from liability of civil damages, in case of violation of an individual's federal constitutional rights, of which a reasonable person would have known. The defence of qualified immunity is developed by the US Supreme Court, in order to shield and protect state and federal officials from the fear of litigation while performing discretionary functions, entrusted to them by law. So, even if a violation of a constitutional right has occurred, the official will be protected, if the said right was not clearly established or the official could have reasonably believed that his conduct was lawful.