Multi-party litigation and complex regulatory matters create privilege management challenges that single-party matters do not. When co-defendants, affiliated entities, or parties with aligned legal interests need to share information and coordinate strategy, the attorney-client privilege that protects individual client communications does not automatically extend to those shared exchanges. The joint defense privilege and the common interest doctrine provide legal frameworks that allow cooperating parties to share otherwise privileged information without waiving protection, but their application, scope, and limitations differ in ways that directly affect document review, privilege log preparation, and discovery strategy.
For litigation teams managing large document populations across multi-party matters, understanding how these doctrines operate in practice is essential to building a defensible privilege review workflow. Misapplying either doctrine, asserting protection where it does not apply or failing to invoke it where it does, can create issues that surface during document production, privilege log challenges, or in camera review.
Key Takeaway
The joint defense privilege and the common interest doctrine both protect shared communications among parties with aligned legal interests, but they apply in different circumstances. The joint defense privilege is most commonly associated with co-defendants coordinating a legal defense, while the common interest doctrine extends more broadly to civil litigation, regulatory matters, and certain transactional contexts. For legal teams managing multi-party matters, understanding these distinctions is critical to designing defensible review workflows, preparing accurate privilege logs, and making consistent production decisions.
What Is the Joint Defense Privilege?
The joint defense privilege is an extension of attorney-client privilege that allows parties with aligned legal interests to share privileged communications without waiving the underlying protection. It is most commonly invoked among co-defendants in criminal matters coordinating a unified defense strategy, although courts have also recognized its application in civil litigation involving parties facing common legal claims.
The privilege allows cooperating parties to exchange confidential communications, discuss defense strategy, and share legal analysis without those communications becoming discoverable by opposing parties. Protection generally applies only to communications made within the scope of the joint defense relationship and in furtherance of the shared legal objective.
Although a written joint defense agreement is not always legally required, it is widely regarded as a best practice. A well-drafted agreement identifies the parties covered, defines the scope of the shared legal interest, establishes how privileged information may be used, and addresses what happens if the relationship later changes. Courts evaluating joint defense privilege claims often consider whether such an agreement exists and how clearly its terms define the parties’ expectations.
What Is the Common Interest Doctrine?
The common interest doctrine is broader than the joint defense privilege. It protects the exchange of privileged information among parties who share a common legal interest, even when they are not co-defendants or formal parties to the same litigation.
The doctrine applies in a variety of legal contexts. In civil litigation, it may protect communications among co-plaintiffs, affiliated entities, or parties facing similar legal exposure. In transactional matters, it is often invoked during mergers and acquisitions, joint ventures, and other transactions where parties must coordinate legal strategy without waiving privilege. It may also apply during regulatory investigations involving organizations with aligned legal interests.
One of the most frequently litigated issues involving the common interest doctrine is distinguishing a shared legal interest from a shared commercial interest. Courts have generally held that a common business objective, standing alone, is not sufficient to support protection under the doctrine. Legal teams asserting common interest protection should be prepared to identify the specific legal interest that the shared communications were intended to advance.
Key Differences and Strategic Considerations
Although the joint defense privilege and the common interest doctrine share similar goals, their practical application differs in several important ways.
Scope of Application
The joint defense privilege most commonly applies to co-defendants coordinating a legal defense in criminal matters and closely related civil litigation. The common interest doctrine extends beyond litigation to include regulatory proceedings and certain transactional matters where parties share a legal interest.
Litigation vs. Transactional Matters
The joint defense privilege is primarily litigation-focused. The common interest doctrine has broader application and is frequently used during mergers and acquisitions, joint ventures, and other commercial transactions where parties exchange privileged legal analysis while pursuing a shared legal objective.
Written Agreements
Although courts do not universally require written agreements, documenting the relationship is considered a best practice under both doctrines. Written agreements clarify the parties involved, define the scope of the shared legal interest, and establish expectations regarding confidentiality and the handling of shared communications.
Privilege Log Preparation
Privilege log preparation requires additional attention when either doctrine is invoked. Entries involving shared communications should clearly identify the parties involved, counsel participating in the communication, and the legal basis supporting the privilege claim. Inconsistent or overly broad privilege log entries are a common source of discovery disputes and requests for in camera review.
The Sedona Conference has published guidance addressing privilege logs, cooperation in discovery, and common interest issues that is frequently referenced by courts and practitioners when evaluating these claims.
How These Doctrines Affect Document Review Workflows
Joint defense and common interest communications require review protocols that address shared communications explicitly before review begins.
Defined Privilege Criteria
Review guidance should explain how reviewers identify communications involving joint defense or common interest parties, how those documents should be coded, what information is required for privilege logs, and when documents should be escalated for attorney review.
Custodian Mapping
Multi-party matters often involve communications from multiple organizations and multiple legal teams. Custodian mapping should account for these relationships so reviewers can consistently identify shared communications throughout the review population.
Privilege Log Standards
Privilege log entries involving joint defense or common interest communications typically require greater specificity than standard privilege claims. Well-defined entry standards established at the outset of the review help improve consistency and support defensible privilege assertions if challenged later in the litigation.
Supporting Defensible Privilege Review
Joint defense and common interest communications require thoughtful review protocols that account for the unique privilege issues presented by multi-party matters. Clearly defined review criteria, attorney oversight, consistent privilege log preparation, and quality control help legal teams apply these doctrines consistently while reducing the risk of privilege challenges during discovery.
Baer Reed partners with law firms and corporate legal departments to provide attorney-led privilege review for complex litigation, regulatory investigations, and other multi-party matters. Our review teams work within client-defined workflows to support consistent privilege determinations, accurate privilege logs, and defensible discovery practices. For support navigating the application of these legal privileges in managed document review, contact Baer Reed today.
