In general terms, privileges are rights held by individuals that permit them to refuse to provide evidence or to prevent certain evidence from being offered against them. Privileges exist only to serve specific interests and relationships; courts give them narrow scope.
Privileges are more or less disfavored by the courts because they run contrary to the principle that all relevant evidence should be admitted in a search for truth. Accordingly, the persons or entities whose confidentiality they are meant to shield or protect can waive their privileges. Individuals who possess a privilege are known as “holders” of the privilege. Often, the nonholder who is a party to a privileged communication must assert the privilege on behalf of the holder.
Congress could not agree on how to make laws regarding privileges, so this area was left up to the courts and to state law to define. Thus, under the FRE, when a party offers evidence on a federal claim the applicable privileges are determined by the federal case law. When a party offers evidence on a state claim, the state’s law of privilege applies. The federal law of privilege is still developing, and the federal courts are usually less tolerant of parties’ claims to privileges than are state courts.