Co-Founder IP: Who Owns What

Two founders build a product together. They ship it. One day they realize the codebase contains patentable inventions. The question nobody asked at the start suddenly matters: who owns the IP?

The answer depends entirely on what paperwork exists. Without an assignment agreement, U.S. patent law gives each co-inventor independent rights to use, sell, or license the invention. Including to your competitor. Without asking permission. Without sharing a dollar.

Last updated: March 2026. This page is informational only and not legal advice. Consult a patent attorney for your specific situation.

Inventorship Is Not Ownership

This is the distinction most founders miss. They are two different legal concepts.

Inventorship	Ownership
Who conceived the invention	Who holds the rights to it
Only natural persons (humans)	Can be a company, individual, or institution
Determined by law (35 U.S.C. 116)	Determined by agreement
Cannot be changed by contract	Transferred via assignment agreement
Getting it wrong can invalidate the patent	Getting it wrong creates ownership disputes

A startup cannot be named as an inventor. Only the people who contributed to the inventive concept qualify. But ownership can and should be assigned to the company through a written agreement.

The gap: Inventorship is automatic. Ownership is not. If you never signed an assignment agreement, each inventor individually owns an undivided interest in the entire patent.

Who Qualifies as an Inventor

The Federal Circuit established a three-part test in Pannu v. Iolab Corp. (1998). Each person claiming inventorship must meet all three factors.

1

Significant contribution

Contributed in some significant manner to the conception or reduction to practice of the invention.

2

Not insignificant in quality

The contribution is not insignificant when measured against the full invention.

3

More than existing knowledge

Did more than merely explain well-known concepts or the current state of the art.

Common misconceptions

Writing the code makes you the inventor. Not necessarily. The inventor is whoever conceived the inventive concept, not necessarily who implemented it.
CEOs are automatically inventors. Only if they contributed to the conception. Funding, managing, or directing the project does not count.
Contributions must be equal. They don't. Joint inventors can contribute to different claims and in different amounts. They don't need to work together or at the same time.
AI can be an inventor. No. The USPTO's 2025 guidance confirms only natural persons qualify. AI is a tool, not an inventor.

The Default Rules Are Brutal

When two co-founders build together and never sign an IP assignment, here is what the law says.

Under 35 U.S.C. 262, each joint owner of a patent may independently:

License to anyone

Including your direct competitor. Without asking permission from the other co-owner.

Keep all the money

No duty to account profits to the other co-owner. Every dollar they make is theirs.

Sell the technology

Make, use, sell, or import the patented invention anywhere in the United States.

Give it away

Make the technology freely available to everyone. Destroying its value for both of you.

This is not theoretical. In Schering Corp. v. Roussel-UCLAF (1997), a co-owner of a pharmaceutical patent quietly licensed it to a company that the other co-owner was actively suing for infringement. The Federal Circuit upheld their right to do it.

The enforcement problem: You cannot sue for patent infringement without all co-owners joining as plaintiffs. One holdout co-owner can block enforcement entirely. Your patent becomes unenforceable if your co-founder refuses to participate.

How Patents Differ from Copyright

If you've dealt with copyright in open source or creative work, patent co-ownership works differently in ways that matter.

	Patent Co-Ownership	Copyright Co-Ownership
Profit sharing	No duty to share profits	Must account to co-owners for profits
Licensing	Can license independently, no consent needed	Can license independently, must share revenue
Exclusive licenses	Cannot grant without all co-owners' consent	Cannot grant without all co-owners' consent
Enforcement	All co-owners must join as plaintiffs	Single co-owner can sue independently
Threshold	Even minor inventive contributions qualify	Must intend contributions to be inseparable

The patent rules are harsher. No profit sharing, no ability to sue alone, and a lower bar for qualifying as a co-owner. This makes unresolved patent co-ownership more dangerous than copyright co-ownership.

What Happens When a Co-Founder Leaves

Without an agreement

They retain their ownership share of any patents they're named on
They can license or sell their rights to a competitor
They can start a competing company using the patented technology
They have no obligation to cooperate with future patent filings
You cannot remove their name from existing patents

With proper agreements

IP remains with the company regardless of who leaves
Post-departure cooperation clauses require assistance with patent prosecution
Work product belongs to the company upon creation
Non-compete clauses prevent immediate competition (jurisdiction-dependent)
Equity vesting protects against early departures

According to Harvard Business School research on 10,000 founders, 65% of high-potential startups fail due to co-founder conflict. The IP question is one of the most common triggers. Startups with proper documentation cut their fallout rate significantly.

The $157.5 Million Lesson

Co-founder IP disputes are not edge cases. They happen to companies of every size.

Snapchat ($157.5M)

Reggie Brown, the third co-founder, claimed he was ousted without credit or compensation for his contributions, including work on patent filings. Snap Inc. settled for $157.5 million, disclosed in their 2017 IPO filing.

Facebook ($65M)

The Winklevoss twins alleged that Zuckerberg used source code he was hired to create for ConnectU. Settled for approximately $65 million in 2008. Separately, Eduardo Saverin's ownership was diluted from 30% to under 10%, with all IP and voting rights transferred.

Schering v. Roussel-UCLAF

Co-owners of a pharmaceutical patent. One co-owner quietly licensed the patent to the very company the other was suing for infringement. The court upheld their right to do it under 35 U.S.C. 262.

The pattern: These disputes all share the same root cause. IP ownership was not clearly documented at the start. By the time it mattered, the only resolution was litigation or settlement.

The Fix: What to Do Right Now

Eight steps that cost almost nothing compared to the alternative.

1

Sign an IP assignment agreement

All IP created for the startup (past and future) should be assigned to the company. Use a CIIA (Confidential Information and Invention Assignment) agreement. Free templates are available from Cooley GO and Orrick.

2

Disclose pre-existing IP

Each founder lists what IP they're bringing into the company. Side projects, prior inventions, open source contributions. Anything not on the list stays personal. Anything on the list gets assigned.

3

Determine inventorship accurately

Only list true inventors on patent applications using the Pannu factors. Do not add names for courtesy, equity, or political reasons. Wrong inventorship can invalidate the entire patent.

4

File provisional patents early

At $65 (micro entity) to $325 (large entity), provisionals are the cheapest protection available. They establish a priority date and give you 12 months to decide whether to invest in a full patent. Read our PPA strategy guide.

5

Create a founders' agreement

Cover equity splits, vesting schedules (standard: 4-year with 1-year cliff), IP ownership, roles, departure terms, and dispute resolution. This is the document that prevents the $157.5 million conversation.

6

Include post-departure cooperation clauses

Require departed founders to assist with patent prosecution, litigation, and IP due diligence. Without this clause, a former co-founder can simply refuse to help.

7

Document inventive contributions

Keep records of who contributed what to which inventions. Lab notebooks, commit histories, design documents, Slack threads. This protects against future inventorship disputes and supports patent prosecution.

8

Scan your codebase now

You can't protect what you don't know you have. Run a free scan to find out what patentable inventions are hiding in your code. Then you'll know what needs protection before the ownership conversation becomes urgent.

Frequently Asked Questions

What if we already have patents without an assignment agreement?

You can sign an assignment retroactively. Both co-inventors execute an assignment transferring their rights to the company. Record the assignment with the USPTO. The sooner this happens, the cleaner the ownership chain. If a co-founder has already left, this becomes significantly harder to negotiate.

What if we listed the wrong inventors on a patent?

Inventorship can be corrected under 37 CFR 1.48, provided the error was made without deceptive intent. You can add, remove, or reorder inventors. The process works for both provisional and non-provisional applications. But it costs time and money. Getting it right the first time is better.

Does a 50/50 equity split mean 50/50 IP ownership?

No. Equity and IP ownership are separate legal concepts. Without an assignment agreement, IP ownership follows inventorship, not equity percentages. A co-founder with 10% equity who conceived the core algorithm has the same patent rights as a co-founder with 90% equity.

What about code written before the company was formed?

Pre-incorporation IP belongs to the individual who created it. The company has no automatic claim to work done before it existed. This is why pre-existing IP disclosure is critical. Each founder should list what they're contributing, and the assignment agreement should explicitly cover pre-existing work.

Do investors care about IP assignment?

Yes. Clean IP assignment is table stakes for institutional investment. VCs and accelerators (including Y Combinator) require it before funding. A messy IP ownership chain is a due diligence red flag that can kill a deal or reduce your valuation.