Attorney work product privilege permits attorneys to withhold from production documents and other tangible things prepared in anticipation of litigation by or for another party or its representative. See: Fed. R. Civ. P. § 26(b)(3). As with attorney-client privilege, work product privilege does not protect underlying facts.
See also: Hickman v. Taylor, 329 U.S. 495 (1947).
However, work product privilege may be overcome if there is a substantial need for materials to prepare the case and the opposing party cannot reasonably obtain their substantial equivalent by other means. For instance, if there is no contemporaneous record and no witnesses to interview, the court may not provide work product privilege.
Work product privilege may be waived when an attorney discloses the work product to a third party in a way that creates a significant likelihood that an adversary or potential adversary in the anticipated litigation will obtain it. See U.S. v. Stewart, 433 F.3d 273 (2d Cir. 2006). This is based on the idea that opposing counsel should not be able to prepare a case on borrowed wits, and only disclosures of work product that are inconsistent with the adversarial system of litigation are contrary to the purposes for which work-product is granted.
For more on the work product doctrine, see this National Law Review article.
[Last updated in December of 2021 by the Wex Definitions Team]