Joint Defense Agreement
A pact letting separately represented parties with aligned legal interests share privileged material without waiving protection.
A joint defense agreement, often called a common interest agreement, allows separately represented parties who share a common legal interest in a matter to exchange privileged communications and work product without waiving those protections as to third parties. It is most common among co-defendants facing the same claim, but it can also cover plaintiffs pursuing related theories, or parties who are not yet co-litigants but share exposure to the same investigation or potential lawsuit. The key requirement is a genuinely common legal interest - a shared business interest or general alignment of goals is not enough on its own.
Courts generally require the interest to be legal rather than purely commercial, and most require that the shared communications relate specifically to the common legal strategy rather than general business matters. A written agreement is not strictly required everywhere the doctrine is recognized, but it is standard practice because it creates a clear record of when the arrangement began, what it covers, and what obligations each party's counsel owes to the group, including confidentiality duties that can survive even if a member later leaves the group or its interests diverge from the others.
The doctrine carries real risk alongside its benefit. If the parties' interests later diverge - one co-defendant decides to cooperate with the government, or settle on terms adverse to the others - questions arise about what that party can disclose and whether it remains bound by confidentiality obligations to former group members. Courts have also held that a party cannot use privilege or work product acquired through a joint defense agreement against another former member of the same group, since that would undermine the candor the doctrine is meant to protect.
How it actually shows up
Co-defendants in complex commercial, product liability, or white-collar matters use joint defense agreements to coordinate strategy, share expert analysis, and present a unified position without giving up their individual privilege protections. Counsel draft these agreements carefully at the outset because a poorly scoped one can create exactly the waiver risk it was meant to avoid if a member's interests shift later.
- Is a joint defense agreement the same as common interest privilege?
- They are closely related, and the terms are often used interchangeably, but common interest doctrine is the underlying legal protection while a joint defense agreement is typically the written contract documenting the parties' shared interest and confidentiality obligations. Some jurisdictions recognize the doctrine even without a written agreement, though having one is still standard practice.
- What happens if co-defendants in a joint defense agreement later have a falling out?
- The privilege and work product protection generally survive as to third parties, but the departing or adverse party typically remains bound by the confidentiality obligations it took on and cannot use information obtained through the agreement against former group members. Courts scrutinize these disputes closely because they implicate both privilege law and contract law.
- Does a joint defense agreement require a genuinely common legal interest?
- Yes. Courts require the interest to be legal, not just a shared business or reputational goal, and the shared communications must actually relate to the common legal strategy. An agreement built on a vague or purely commercial alignment risks being found invalid, which would expose the shared communications to discovery.
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