The common interest doctrine can sometimes protect communications between separately represented clients that would otherwise trigger a waiver – if those clients share an identical (or nearly identical, in some courts) legal interest. Nearly every court applies the doctrine only if the clients are in or reasonably anticipate litigation. And even then, about half of them fail for one reason or another.

In Fellowship of Christian Athletes v. San Jose Unified School District Board of Education, Case No. 20-cv-02798-hsg (VKD), 2022 U.S. Dist. LEXIS 73339, at *7 (N.D. Cal. Apr. 21, 2022), the court recited one basic nearly universally-recognized attribute of the common interest doctrine – warning that "[t]he doctrine does not create a privilege but comes into play only if a privilege or protection already covers the material disclosed to the third party." That certainly is true about pre-existing historical documents that common interest participants share with each other. But of course in the right context, the common interest doctrine can also protect contemporaneous communications between the participants' lawyers. For those, the doctrine does create a privilege.

That frequently recited erroneous statement seems harmless. Perhaps the participants' lawyers rely on the work product doctrine when withholding those contemporaneous communications. And no court seems to have upheld a challenge to withholding such communications in a setting where the court acknowledges the common interest doctrine’s general applicability.