Common Interest
A shared legal interest held by multiple parties, such as co-owners of property or parties with a shared litigation privilege (common interest doctrine preserves attorney-client privilege when shared counsel communicate).
While straightforward in theory, many businesses fail to actively track obligations tied to this concept - often resulting in missed deadlines, unintended renewals, penalties, or loss of contractual rights.
US Law · For business owners and foundersWhat is a Common Interest?
A common interest is a shared legal right or entitlement held by multiple parties. In property law, common interest refers to joint ownership or a shared stake in real or personal property (e.g., co-owners of a house or partners in a business). In litigation and privilege law, common interest refers to the "common interest doctrine," which allows multiple parties (often defendants or co-defendants) to share the same attorney or share attorney-client privileged communications without waiving privilege.
The common interest doctrine is critical in litigation. When multiple parties (such as co-defendants or parties on the same side of a dispute) retain counsel to advance a shared legal interest, communications between those parties and their respective counsel can remain privileged even if shared among all parties. Without this doctrine, sharing attorney advice with co-defendants would "waive" privilege against third parties.
Common interest also arises in transactional contexts: co-signers of a loan share a common interest in the loan agreement; co-investors in a fund share a common interest in fund governance; joint venture partners share common interest in the venture's success and legal compliance.
In practice, many teams rely on a contract expiry tracking system to stay on top of dates and obligations tied to clauses like this.
Key Elements
Shared Legal Objective
All parties must share a common legal interest, goal, or objective - whether defending against a claim, enforcing a contract, or managing joint property. The interest must be legally relevant, not just factual.Communication Regarding Shared Interest
For the common interest doctrine to apply in privilege context, communications must be about the shared legal interest. Communications about unrelated matters do not qualify.Reasonable Expectation of Privilege
When parties share privileged materials, they must have a reasonable expectation that the privilege will be maintained. Sharing with a party without prior agreement about confidentiality may result in loss of privilege.No Waiver Between Co-Interested Parties
Disclosing privileged information to co-interested parties does not waive the privilege as to third parties. However, it may limit privilege if the parties later become adversaries.Termination of Common Interest
Once the common interest ends (e.g., litigation concludes, partnership dissolves), the parties may no longer rely on the doctrine to keep shared communications privileged between themselves.Real-World Example
Two co-defendants in a product liability lawsuit hire separate counsel but both counsel agree to keep a shared litigation team. They exchange attorney work product memos analyzing the liability exposure and defense strategy. A settlement offer comes in and one defendant settles. The settled defendant is later deposed by the plaintiff.
Because both defendants shared a common legal interest during the lawsuit, the communications between them and their counsel remain privileged as between the two parties. However, once one defendant settled and their interests diverged, the common interest doctrine may be tested if the settled defendant is asked to testify about strategy discussed while the common interest existed. The result varies by jurisdiction, but the initial sharing was protected by the doctrine.
This is why many businesses adopt automated deadline tracking to ensure no critical dates are missed before they pass.
Sample Clause Language
Common Interest Acknowledgment in Joint DefenseWatch Out For
Loss of privilege when interests diverge
The common interest doctrine only protects communications made while the common interest exists. Once two parties become adversaries (e.g., one co-defendant settles), shared materials may lose privilege as between them.Sharing with non-parties or mixed groups
If you share privileged materials with a party who does not share your legal interest, or if your group includes both interested and non-interested parties, privilege may be lost or significantly limited.No blanket privilege for all communications
Only communications made in furtherance of the common legal interest are protected. Casual conversations, business discussions unrelated to the shared interest, or communications about unrelated matters do not qualify.Timing and prior agreement matter
The common interest doctrine works best when parties have a pre-existing agreement that they will share counsel or communications. Retroactively claiming common interest without clear prior understanding is risky.Don't let common interest deadlines catch you off guard
Key dates tied to common interests - renewal windows, expiry cutoffs, notice periods - can easily slip through the cracks when tracked manually. Missing them triggers automatic extensions, penalties, or lost rights. ExpiryEdge tracks every critical deadline and sends automated reminders before they're due - so nothing slips.
Instead of relying on spreadsheets or manual follow-ups, a centralized renewal reminder system ensures every deadline is visible, tracked, and actioned automatically.
How to Use This in Your Favor
Use formal joint defense agreements
Before sharing privileged materials with co-parties, enter into a written joint defense agreement (also called a common interest agreement) that explicitly acknowledges the shared interest and creates mutual obligations of confidentiality.Mark shared materials clearly
Label all shared privileged communications with "Joint Defense - Privileged and Confidential" and list the co-parties. This makes the protective intent clear and supports privilege arguments.Related Terms
Frequently Asked Questions
Does the common interest doctrine allow unlimited sharing?
No. You can only share materials with parties who share your legal interest, and only for purposes of advancing that shared interest. Sharing beyond these bounds waives privilege.
What happens if a co-party violates the confidentiality agreement?
If a co-party discloses shared privileged materials to opposing counsel or a third party, you may have a breach of contract claim against that co-party and can ask the court to exclude the improperly disclosed materials from evidence. However, privilege is still lost for all purposes as to the third party.
Can a third party claim the common interest doctrine?
No. The doctrine only protects communications between parties who share the common interest. A third party who overhears or is accidentally copied on a privileged email cannot claim protection under the doctrine.