You Invented It Together. Now Write It Down.

Two engineers solve a problem over eighteen months of evenings and file with both names on the application. Nobody discusses ownership because the relationship is good and the patent is years from mattering. Then one takes a job at a large company, or moves overseas, or wants out, or dies. At that point the collaboration is governed entirely by a default rule neither of them has read, and it is worse than they imagine.

The fix is a document signed while everyone still likes each other. It costs a few thousand dollars and is the highest-return legal work an inventing pair will ever do.

Inventor and Owner Are Two Different Things

Inventorship is a legal determination, not a courtesy. Under US law an inventor is someone who contributed to the conception of at least one claim in the issued patent. Conception means the definite and permanent idea of the complete operative invention, not the work of building it.

The machinist who fabricated parts to your drawings is not an inventor. The investor who funded the work is not an inventor. The colleague who suggested a different sensor, where that sensor became a claim limitation, probably is. Getting it wrong in either direction is a defect in the patent: US law allows correction of inventorship absent deceptive intent, but an adversary in litigation will spend real money trying to prove intent existed. Determine inventorship claim by claim, after the claims are drafted, with the patent attorney. It shifts whenever claims are amended during prosecution, which is one more reason to understand how patent claims actually work.

Ownership is separate. Inventors own their invention initially, but ownership moves by written assignment. A patent can list three inventors and be owned entirely by a company that employs none of them.

The Default Rule, and Why It Is a Trap

When two inventors file together and never assign anything, US law makes each of them a joint owner of an undivided interest in the entire patent. Not half the patent each. All of it, each.

The consequences catch people completely by surprise:

  • Either co-owner can license the patent to anyone, without the other's consent. Your co-inventor can grant a non-exclusive license to your largest competitor on Monday morning and is under no obligation to tell you.
  • Neither owes the other an accounting. A co-owner who makes and sells the patented product, or collects royalties, can keep every dollar. There is no default profit-sharing.
  • Exclusivity becomes impossible to sell. You cannot grant an exclusive license alone, because your co-owner retains the right to practice and to license. That kills most serious licensing deals outright.
  • Every co-owner must join an infringement suit. One co-owner who refuses to participate can block enforcement entirely, and there is generally no way to compel them. A patent that cannot be enforced is decoration, whatever the infringement playbook says.
  • Interests pass on death and divorce. Your co-owner's share can end up with heirs who have no interest in the project and no obligation to cooperate.

This default is a US rule. Several other jurisdictions require co-owner consent to license, so an international portfolio can be governed by contradictory defaults. Contract around it and the problem disappears.

Check the Employer Question First

Before writing anything, establish that both inventors are free to own what they invented. If one developed their contribution using employer time, equipment, or subject matter within their job scope, the employer may own that share outright, and many employment agreements assign inventions automatically. State law varies on how far those clauses reach. Resolve it before filing, and read whether your employer owns your invention alongside your actual agreement. Finding a third party in the chain of title during diligence is a deal-stopping event.

What Belongs in a Co-Inventor Agreement

  • Ownership shares. Explicit percentages, and not necessarily equal. Weight technical contribution, capital contributed, and future work committed. A 50/50 split chosen to avoid an awkward conversation causes a worse conversation later, for the same reasons set out in how to split equity between co-founders.
  • Cost sharing. Who funds filings, prosecution, foreign entry, and renewals, and what happens when someone stops paying. The usual mechanism is dilution: a non-paying party's share reduces proportionally. Attach a schedule of expected costs so nobody claims surprise, drawing on real patent cost figures and the maintenance fee timetable.
  • Decision rights. Which actions need unanimity (sale, exclusive license, abandonment) and which need only a designated lead (routine prosecution responses). Without this, prosecution stalls on unreturned emails.
  • A consent requirement for licensing. This is the clause that overrides the dangerous default. No co-owner may license, assign, or encumber without written consent.
  • Exit and deadlock. Right of first refusal on a departing party's share, a valuation method, and a tiebreaker such as a shotgun clause or a named neutral.
  • Confidentiality. Mutual, and surviving the relationship. Until filing, either party's disclosure destroys novelty for both, which is the practical point of an inventor's NDA.

The Clean Solution: One Entity Owns Everything

The best structure is usually not a co-ownership agreement at all. Form a single entity, have both inventors assign 100 percent of the patent rights to it, hold percentages as equity instead, and record the assignment with the USPTO.

Everything then becomes routine corporate governance rather than exotic patent law. The entity signs licenses with one signature and sues in its own name. Shares transfer without touching the chain of title. Vesting schedules, buy-sell provisions, and deadlock mechanisms are standard clauses any business attorney drafts weekly. Investors can invest. And the patent file stays clean. The entity choice is straightforward for most inventing pairs and is covered in LLC versus sole proprietorship for inventors.

Sort the Ownership Before the Filing

Projects House works with inventing teams from the technical side, defining who contributed what to which feature and producing the documentation that supports a defensible inventorship determination. Describe your project and your collaboration through the contact form.