Joint defense groups: economics, formation, and the privilege framework

An NPE files one complaint against twenty defendants on a single patent. Each defendant, working alone, would spend $3M-$5M defending through trial. The same twenty defendants, coordinating through a joint defense group (JDG), can run the same defense for $200K-$500K each.

That arithmetic is the single biggest lever in multi-defendant patent litigation. It only works if the legal scaffolding — specifically the common-interest privilege — is set up correctly. Without it, every email between defendants is a privilege waiver waiting to be produced in discovery.

This article is the JDG playbook: what it is, why it works, the privilege framework that makes it legally possible, how to draft the agreement, how to allocate costs, how to govern the group, how to share IPR work, and how to manage the free-rider problem that wrecks half of JDGs that fail.

What a joint defense group actually is

A JDG is a formal common-interest arrangement among co-defendants (and sometimes interested non-parties) who share a defense against the same plaintiff on the same or substantially overlapping patents. It is not a partnership. It is not a joint venture. It does not create a new legal entity. It is a contractual and privilege-protected information-sharing structure.

What members typically share:

Prior-art research. One commercial search costs $10K-$25K; ten defendants split it.
Invalidity contentions and claim-construction briefs. Drafted once, edited per defendant.
An IPR petition. One filing, multiple petitioners (or one petitioner with funding from others).
Expert witnesses. A technical expert costs $50K-$300K through trial; shared, that drops per-defendant.
Damages experts and analyses. Especially around the asserter's prior settlements and licensing patterns.
Strategic intelligence about the plaintiff: counsel patterns, settlement floors, prior pleadings, deposition history.
Settlement coordination (this is the messiest part — see below).

What members do not share:

Their individual product information (each defendant's accused product is its own non-infringement story).
Their settlement amounts (each defendant negotiates separately; settlement terms are usually confidential).
Their internal strategic decisions (whether to settle, how much to pay, when to walk).

The shared work is the common defense; the unshared work is the individual defense. The line between the two is the whole legal architecture of the JDG.

Why the economics work: cost asymmetry

The NPE business model assumes uncoordinated defendants. The plaintiff files one complaint, recycles the same infringement allegations across dozens of defendants, and collects settlements priced below each defendant's cost-of-defense. (How troll campaigns work →)

The defendant's cost-of-defense is the anchor for that settlement number. If you can credibly drop it from $5M to $500K, the plaintiff's pricing power collapses.

A rough cost map for a 10-defendant JDG running a competent defense through claim construction:

Work product	Solo cost	JDG cost (10 def.)	Per-def. savings
Prior-art search (commercial)	$15K	$15K	$13.5K
Invalidity contentions draft	$80K	$100K	$70K
IPR petition	$300K-$500K	$400K	$260K-$460K
Claim construction brief	$250K	$300K	$220K
Technical expert (through Markman)	$150K	$200K	$130K
Damages expert	$80K	$120K	$68K
Lead-counsel coordination	n/a	$150K	-$15K
Total shared	$875K	$1.285M	~$750K per def.

Add each defendant's individual work — answer, individual non-infringement contentions, their own discovery responses, deposition prep — and a typical per-defendant total drops from $3M-$5M solo to $300K-$700K in a 10-way JDG. Bigger groups push the number lower still, with diminishing returns past 15 members.

The Innovatio Wi-Fi cases are the classic example. Innovatio IP Ventures asserted three patents covering 802.11 Wi-Fi against hundreds of defendants — hotels, coffee shops, retailers, and the manufacturers behind them. The manufacturer-led JDG (Cisco, Motorola, Netgear, SonicWall) coordinated invalidity, claim construction, and a single damages framework. The smaller defendants — many of whom would have settled for nuisance values solo — got the benefit of a multi-million-dollar invalidity attack they didn't have to fund alone. (The economics of multi-defendant campaigns →)

The privilege moat: common-interest doctrine

The legal scaffolding that makes a JDG possible is the common-interest privilege — sometimes called the joint-defense privilege. Without it, the moment two defendants share a confidential analysis of the patent, both have waived attorney-client privilege as to that analysis. Discovery would force production. The whole structure would be a self-inflicted privilege wound.

What common-interest privilege does

Under federal common law (and most state laws), the common-interest doctrine extends existing privilege to communications between separately-represented parties who share a common legal interest. It does not create a new privilege. It protects communications that were already privileged from waiver when shared with aligned parties.

To qualify, three elements typically have to be present:

A common legal interest — not just a common commercial interest. Sharing a defense against the same patent on the same allegations is a paradigm common legal interest. Two competitors who just happen to dislike the same plaintiff is not.
Communications made in furtherance of that interest — strategy, analysis, prior-art assessment, claim construction. Not general business communications.
An intent to maintain confidentiality — usually evidenced by a written common-interest agreement, but a written agreement is not strictly required in every circuit.

What it covers — and what it doesn't

Covered (when properly invoked):

Attorney-to-attorney communications across the JDG.
Memoranda and analyses prepared by one defendant's counsel and shared with the group.
Work product (e.g., expert draft reports) shared in furtherance of the common defense.
Joint meeting notes where strategy is discussed.

Not covered, even inside a JDG:

Pre-existing facts. The privilege protects communications, not underlying facts. If a defendant's engineer happened to attend a 2008 trade show where the asserted invention was demoed, that fact is discoverable regardless of who knows about it.
Communications outside the common-interest scope. If two JDG members start discussing a separate commercial dispute between them, that's not protected.
Information that wasn't privileged to begin with. Public documents, previously-disclosed materials, business records.
Communications after a member exits the JDG. Once a defendant settles and leaves, post-exit communications aren't protected.

Circuit splits and danger zones

The common-interest doctrine is federal common law for federal-question cases (which includes all patent litigation). But the contours vary by circuit:

Most circuits require a "palpable" common legal interest, not just shared commercial interest. In re Teleglobe Communications Corp. (3d Cir. 2007) is the canonical case.
A minority approach (some courts in the Second and Ninth Circuits) requires actual pending or anticipated litigation, not just shared concern about a patent.
Strict-construction courts require written agreements; functionalist courts accept conduct.

The practical takeaway: get the written agreement signed before any sensitive material crosses defendants' boundaries. The cost of drafting is trivial; the cost of a privilege fight if the relationship is challenged is enormous.

The common-interest agreement

The written agreement (sometimes called a "joint defense agreement" or "JDA") is the foundation document. Standard contents:

flowchart TD
  A["Joint Defense Agreement"] --> B["Recitals: shared interest<br/>in same patent litigation"]
  A --> C["Scope of common interest<br/>and shared topics"]
  A --> D["Confidentiality obligations<br/>and use restrictions"]
  A --> E["Withdrawal procedures<br/>and post-exit duties"]
  A --> F["Cost-sharing framework<br/>(if included)"]
  A --> G["Lead counsel / committee<br/>governance"]
  A --> H["No conflict waiver<br/>(usually)"]
  A --> I["Choice of law<br/>and dispute resolution"]

  style A fill:#fff7ed,stroke:#c2410c,color:#1c1917
  style D fill:#dbeafe,stroke:#1e40af,color:#1c1917
  style E fill:#fee2e2,stroke:#be123c,color:#1c1917

Specifically:

Recitals. Identifies the parties, the litigation, the asserted patents, and the common legal interest in invalidating, narrowing, or defeating the patent.
Scope. What topics are within the common interest. Usually: validity, claim construction, prior art, expert work on those topics, plaintiff intelligence. Sometimes: damages methodology. Rarely: individual non-infringement positions (which can conflict between defendants).
Confidentiality. All shared materials are confidential. Each member can use them only for the common defense. No external disclosure without unanimous consent.
Withdrawal. Members can withdraw on notice. On withdrawal, the member must return or destroy shared materials and remains bound by confidentiality. Importantly, withdrawal does not waive privilege as to communications made while the member was in the group.
Cost-sharing. Either inside the JDA or in a separate "common-defense fund" agreement. (Some practitioners keep these separate — the JDA is the privilege document; the fund agreement is the economic document.)
Governance. Who decides what gets briefed, when, and on whose budget. Usually a steering committee of lead defendants.
No conflict waiver. The agreement typically clarifies that each defendant's counsel represents only that defendant, not the JDG as a whole, and the agreement does not create joint representation.
Choice of law and dispute resolution. Usually the law of the litigation venue; disputes resolved through arbitration or the litigation court.

Who drafts: usually lead counsel for the largest defendant, circulated to all members for negotiation. Sometimes one of the boutiques known for plaintiff-side NPE defense (Erise, Haynes Boone, Fish & Richardson on the defense side, McKool Smith for larger campaigns) drafts a template that gets reused across multiple JDGs.

When it gets signed: before any privileged material is shared. A common mistake is to start sharing prior-art research while "still negotiating" the JDA. That sharing isn't protected. Sign the agreement first; share second.

Cost allocation models

The single most common reason JDGs collapse is a fight over money. Four allocation models are the standard menu.

1. Equal split

Each member pays an equal share of every common expense. Simple, transparent, and works well when defendants are roughly equivalent in size and exposure (e.g., the Innovatio hotel-defendant pool).

Problems:

Punishes small defendants when the group has Apple, Microsoft, and a 30-person SaaS company in it.
Big defendants get a windfall: they pay 1/10 of the cost for benefits worth 10x more to them than to the small defendants.

2. Weighted by exposure

Each member pays a share proportional to its damages exposure, calculated using a rough revenue-times-royalty-rate proxy. Mathematically fair; politically miserable to negotiate (no defendant wants to admit high exposure).

Common workaround: use a public revenue proxy (most recent annual revenue from public filings or industry estimates) rather than asking each defendant to disclose internal numbers.

3. Weighted by deal size (or "tiers")

Defendants are slotted into tiers based on size, with each tier paying a fixed share. A typical structure:

Tier	Description	Share
Tier 1	Revenue > $1B	40% (split among tier members)
Tier 2	Revenue $100M-$1B	35%
Tier 3	Revenue $10M-$100M	20%
Tier 4	Revenue < $10M	5%

Easier to negotiate than exposure-weighted because tier membership is observable. Most large JDGs end up here.

4. Opt-in by workstream

The JDG identifies discrete workstreams — IPR petition, prior-art search, claim construction expert, damages expert, Markman briefing — and members opt in (and pay) per workstream. A defendant uninterested in IPR can skip that bucket; a defendant uninterested in damages expert work can skip that.

Best for heterogeneous JDGs where members have different exposures and different appetites. Worst for governance — each workstream becomes its own negotiation.

In practice, large NPE JDGs typically combine tier-based allocation (for core work) with opt-in workstreams (for non-core or specialty work).

Governance: lead counsel and committees

A JDG of 5 defendants can govern itself by consensus. A JDG of 25 cannot. The governance structures that scale:

flowchart TD
  AC["All members (info recipients)"] -.-> SC["Steering committee<br/>(3-5 largest defendants)"]
  SC --> LC["Lead counsel<br/>(one defendant's lead firm)"]
  LC --> WG1["Workgroup: Invalidity<br/>+ prior art"]
  LC --> WG2["Workgroup: IPR"]
  LC --> WG3["Workgroup: Markman<br/>+ claim construction"]
  LC --> WG4["Workgroup: Damages"]

  style SC fill:#fff7ed,stroke:#c2410c,color:#1c1917
  style LC fill:#dbeafe,stroke:#1e40af,color:#1c1917

Lead counsel is one defendant's outside counsel, designated to coordinate group work, send group communications, and (usually) sign briefs as the "lead" defendant. The role is logistical, not representational — lead counsel still represents only their own client. Defendants take turns lead-counseling specific workstreams.
Steering committee is typically 3-5 of the largest defendants. The committee makes binding decisions on budget and direction; the broader group is informed and can opt out of specific workstreams.
Workgroups are subgroups of attorneys working on specific deliverables: an invalidity team, an IPR team, a Markman team, a damages team. Each has a designated workgroup lead who reports to lead counsel.
Settlement coordination — discussed below — is often handled outside the steering structure because it's the most conflict-prone topic.

The settlement-coordination problem

This is where JDGs get messy. Each defendant's settlement decisions are individual, confidential, and made in the defendant's own interest. But the order in which defendants settle matters enormously:

The first defendant to settle often sets the floor. If Apple settles for $2M, every subsequent settlement gets benchmarked against that — sometimes up, sometimes down.
The last defendants to settle face a weakened plaintiff. If 18 of 20 defendants have settled, the plaintiff's economics have shifted; the remaining defendants can often negotiate down.
But if the JDG is leaning on a shared IPR, defectors who settle early may withdraw funding from the IPR, weakening the petition for the holdouts.

Standard JDG practice: settlement decisions are not discussed in JDG meetings. Some agreements explicitly carve settlement out of the common-interest scope. Defendants are bound by confidentiality not to disclose settlement amounts to plaintiff or to other defendants. Information leakage about who is negotiating happens informally, through counsel networks, and is one of the murkier ethical zones in patent litigation.

IPR sharing: one petition, multiple petitioners

Inter partes review is the single highest-value coordinated workstream in most JDGs. The structural rules:

Multiple parties may join an IPR. Under 35 U.S.C. § 315(c), once an IPR is instituted, additional parties can move to join within one month. Joinder is discretionary; the PTAB grants it routinely for parties asserting the same grounds.
A single IPR petition can name multiple petitioners. Some JDGs file a single petition with all members as named petitioners; others have one named petitioner and the rest join via § 315(c).
Estoppel attaches per petitioner. Under 35 U.S.C. § 315(e), each petitioner is estopped from raising in district court any invalidity argument that was raised or reasonably could have been raised in the IPR. (IPR estoppel deep dive →)

The estoppel point is the trickiest part. Every JDG member who joins an IPR — whether as a named petitioner or as a joinder party — is bound by its estoppel. If the IPR loses, those members can't re-litigate the same prior art in district court.

flowchart TD
  S["JDG considers IPR"] --> Q1{"Strong prior art<br/>in JDG hands?"}
  Q1 -->|"No"| OUT["Skip IPR.<br/>Focus on Alice § 101<br/>or non-infringement"]
  Q1 -->|"Yes"| Q2{"Who joins<br/>as petitioner?"}
  Q2 --> NP["Named petitioners<br/>(maximum estoppel<br/>maximum cost share)"]
  Q2 --> JP["Joinder petitioners<br/>(some estoppel<br/>some cost share)"]
  Q2 --> NF["Non-funders<br/>(no estoppel<br/>but no IPR benefit<br/>= free riders)"]

  style NP fill:#d1fae5,stroke:#047857,color:#1c1917
  style JP fill:#fff7ed,stroke:#c2410c,color:#1c1917
  style NF fill:#fee2e2,stroke:#be123c,color:#1c1917

The complication that the Apple Inc. v. VirnetX line of cases highlighted: when a JDG runs multiple IPR petitions on the same patent, the Fintiv factors and the PTAB's discretionary-denial framework can lead to denial of later petitions. Coordinating filing timing across a JDG is now a real strategic concern.

Microsoft's IPR campaign against Uniloc in the late 2010s is the modern blueprint for coordinated IPR strategy: Microsoft as named petitioner filing on its own and on behalf of de facto JDGs, accepting estoppel as the cost of doing business in exchange for taking out the underlying patents. The PTAB invalidated multiple Uniloc patents through that effort, and the downstream effect on later assertions was substantial.

The free-rider problem

The hardest political problem in JDGs is the defendant who benefits without paying. Two flavors:

1. The hold-out

The hold-out is named in the same complaint, declines to join the JDG, and benefits from the shared invalidity work anyway. If the JDG's IPR invalidates the patent, the hold-out's case dies for free.

Free-riders can't be prevented entirely. What JDGs can do:

Membership-gate certain deliverables. Internal claim charts, draft expert reports, attorney work product — only members see these. Public filings (IPR petitions, briefs) become available once filed regardless.
Coordinate timing. Time IPR filings so that hold-outs can't free-ride on the JDG's institution decision before they commit.
Use § 315 estoppel as leverage. Some JDGs invite hold-outs to join the IPR on terms that bind them to the estoppel — sharing the benefit only with members who also share the downside.
Settle-and-license carve-outs. Some defendants negotiate settlements that explicitly preclude the plaintiff from later collecting on the patent even if it survives the JDG's IPR.

2. The defector

The defector joins the JDG, learns the group's strategy, and then settles early — sometimes leaking the group's posture to the plaintiff in the course of negotiation.

Standard JDG protections:

Confidentiality survives withdrawal. Members who leave remain bound not to disclose group communications.
No discussion of settlement in JDG meetings. Per above. Settlement positions are individual and outside the JDA scope.
No-poach of common materials. A withdrawing defendant typically must return or destroy group materials (though they can keep their own attorney-work-product based on those materials).

In practice, defection is more common in JDGs that drag through trial. Most JDGs lose 30-50% of their members to settlement by Markman. The structure has to assume attrition.

When a JDG makes sense — and when to go solo

A JDG is overhead. It costs lawyer time, coordination effort, and political bandwidth. The threshold question is whether the savings exceed the overhead.

JDG indicators (strong)

5+ co-defendants on the same patent or substantially overlapping patents.
A clear shared invalidity theory — same prior art, same claim-construction targets, same § 101 attack surface.
High individual defense costs if you went solo ($1M+).
A coordinated plaintiff running a campaign against similar defendants. (Anatomy of a shakedown →)
Defendants of broadly comparable interests — all consumers of the same accused functionality, all running similar products.

Go-solo indicators

Small case — settlement value below $200K-$300K total. JDG overhead exceeds savings.
Niche technology unique to your product, where the shared invalidity work doesn't apply.
Conflicting interests — your non-infringement theory contradicts a co-defendant's. (For example: one defendant argues the claim requires X; another defendant's product has X but argues the claim shouldn't be construed to require X. They can't share a claim-construction position.)
You're an outlier defendant — much larger or much smaller than the rest. Cost allocation will be politically painful either way.
You're going to settle anyway. No point joining the JDG to fund work you'll exit before benefiting from.

Real examples

Innovatio IP Ventures (Wi-Fi cafe defendants, 2011-2014). Innovatio asserted 802.11 patents against hundreds of end users — hotels, cafes, retailers — plus the major Wi-Fi manufacturers. The manufacturer-led JDG took over the defense, secured a damages cap, and settled the case for a fraction of the original demand. The classic "JDG saves small defendants" outcome.
Microsoft IPRs against Uniloc (2017-2021). Microsoft acted as a named petitioner across multiple Uniloc IPR campaigns, sometimes coordinating with informal co-defendant networks. PTAB invalidated several patents; subsequent Uniloc assertions on those patents collapsed.
E.D. Tex. multi-defendant patent suits (ongoing). Eastern District of Texas remains a major venue for NPE filings — though post-TC Heartland much reduced — and most large E.D. Tex. cases involve 10-50 co-defendants who form JDGs by docket position. The Texas plaintiff's bar's recycled-template pleadings against similar accused products make for naturally coherent JDGs.
Lumen View v. FindTheBest (S.D.N.Y. 2014). Smaller scale — a handful of related defendants — but a useful case study in coordinated § 285 fee-shifting strategy. The asserted patent (US 8,069,073) was the basis of one of the first post-Octane Fitness fee awards against an NPE.

A short JDG-formation checklist

If you're a defendant evaluating JDG formation, ranked rough order:

Identify co-defendants. PACER, RPX, Unified Patents, the litigation registry on this site. Pull the plaintiff's filing history.
Have counsel make initial contact. JDG outreach is attorney-to-attorney. Defendants don't reach out to each other directly until the legal framework is in place.
Sign the JDA before sharing anything sensitive. Drafting takes 1-2 weeks. Don't share prior-art research, claim charts, or strategy until executed.
Agree on cost allocation up front. Use tier-based allocation or workstream opt-in. Don't paper this over with "we'll figure it out later" — that's where JDGs die.
Designate lead counsel and a steering committee within 30 days of formation.
Decide on IPR within 60-90 days. The one-year IPR bar runs per defendant from each defendant's individual service date; coordinating filing requires every member's window to still be open.
Establish settlement protocols. Each defendant's individual decision, but agree how the group is informed (usually: minimal disclosure, no joint pressure on settling defendants).
Re-evaluate at each litigation milestone — answer, Markman, summary judgment. Some members will exit; the JDG has to re-stabilize around remaining members.

Bottom line

The math is overwhelming. An NPE files against 20 defendants on one patent; solo, each faces $3M-$5M. Pooled into a JDG, $200K-$500K each — sometimes less. The plaintiff's economic model assumes uncoordinated defendants; coordinating breaks the model.

The legal architecture is the common-interest privilege, formalized in a written JDA, governed by lead counsel and a steering committee, funded through a tier-based or workstream-opt-in cost model, and protected against defectors by confidentiality terms that survive withdrawal.

The hardest political problems are settlement coordination and the free-rider problem. Neither has a clean solution; both have standard practices. JDGs that ignore them die; JDGs that build structure around them survive.

If you've just been served, JDG outreach goes on the Week 3 checklist of the first 30 days. If you're trying to figure out what you're facing in the first place, the demand-letter analyzer or the quiz is the right starting point.

This article is for general education and is not legal advice. The common-interest privilege framework varies by circuit and by court; specific JDA terms should be negotiated with counsel who has run multi-defendant NPE coordination before.