Privilege is waived by voluntary disclosure to a third party, and the scope of the resulting waiver is what makes the decision consequential.
Subject matter waiver. Where disclosure is intentional and the disclosed and undisclosed communications concern the same subject matter, fairness may require production of the rest. Rules limit this in federal proceedings to circumstances where they ought in fairness to be considered together.
Inadvertent disclosure. Protection is preserved where the holder took reasonable steps to prevent disclosure and promptly took reasonable steps to rectify, including following claw-back procedures.
Non-waiver orders. An order under the applicable evidence rule can provide that disclosure in the proceeding does not waive privilege in any other federal or state proceeding. Obtaining one at the start of discovery is inexpensive insurance.
Selective waiver. Disclosure to a regulator has generally been held to waive privilege as against private litigants, and most courts have rejected a selective waiver doctrine. Confidentiality agreements with the agency do not reliably prevent this.
At issue waiver. Asserting reliance on advice of counsel, or putting the state of one’s legal knowledge in issue, waives privilege on that subject.
Practical discipline. Decide in advance what will be disclosed and to whom, segregate legal analysis from factual findings, and never let a partial disclosure happen by accident.