Federal Rule of Evidence 502

The prospect of inadvertently disclosing privileged documents to one's adversary is one of a lawyer's worst nightmares. Before the advent of electronic discovery, when parties reviewed and produced tens of thousands, or even millions of pages of paper, it was an article of faith that every document would be reviewed, and, if found to be privileged, withheld under a substantiated privilege claim. There was a good reason for this: Courts routinely held that the attorney-client privilege was waived in the event of a disclosure, even if the disclosure was inadvertent, with the result that the document could be used by one's adversary. In some cases, the waiver applied to all documents of the same subject matter as the document that had been inadvertently disclosed, a development which could deal a death blow to one's case.