The doctrine that allows separately represented parties with common legal interests to share information with each other and their respective attorneys without destroying the attorney-client privilege. It is also known as the joint defense doctrine.

The common interest doctrine is not a separate privilege, but rather stands as a notable exception to the general rule that the attorney-client privilege does not attach to communications with, in the presence of, or later shared with, third parties. The communications must therefore be intrinsically privileged to deserve protection under the common interest doctrine. A communication that does not itself deserve privilege does not gain that protection when one common interest participant shares it with another.

The common interest doctrine applies only where the common interest participants are actually engaged in a joint effort or strategy to further their common interests. It generally does not apply where the participants merely have common problems or share a desire to succeed in a particular action.

For more information on the common interest doctrine, see Practice Notes, Attorney-Client Privilege: Common Interest Doctrine (Federal) and Data Breaches: The Attorney-Client Privilege and the Work Product Doctrine: Explore Common Interest and Joint Defense Agreements.