Many transactions, litigations or business disputes can involve multiple parties who have different attorneys but aligned interests. As a result, those parties may want to communicate with one another on issues of strategy or planning without risking the waiver of any applicable privileges or immunities. In such a situation, clients and counsel can benefit from the options developed by courts, including by sharing a joint defense or common interest privilege.

The prerequisites, scope and boundaries of the joint defense or common interest privilege can differ significantly, depending on the jurisdiction. State and federal jurisdictions vary over whether they even recognize a joint defense or common interest privilege, as well as to what extent such a privilege applies. To bridge these gaps, many attorneys will pursue a formal written agreement on behalf of their clients, although such an agreement does not always need to be in writing to be enforceable.