It depends on the country and on the contract, and the default is not always the employer. In the United States, the inventor owns the invention unless there is an assignment; an employer gets ownership through a written invention assignment agreement or, absent one, only if the employee was specifically hired to invent that thing. Otherwise the employer may hold a "shop right", a non-exclusive licence to use the invention, while the employee keeps title. Several states, including California under Labor Code section 2870, void clauses that claim inventions made on the employee's own time without company resources and unrelated to the business. In the United Kingdom, section 39 of the Patents Act 1977 gives the employer inventions made in the course of the employee's normal or specifically assigned duties, where an invention might reasonably be expected, and inventions by senior employees with a special obligation to further the business; everything else belongs to the employee, and under section 40 an employee can claim compensation where a patent has been of outstanding benefit to the employer.

Germany's Employee Inventions Act requires the employee to report every service invention in writing; the employer is deemed to have claimed it unless it releases the invention within four months, and must pay the inventor statutory compensation. Sweden's Act on the Right to Employees' Inventions gives the employer rights to inventions within the scope of the employee's duties in exchange for reasonable compensation, with collective agreements often filling in the detail; university teachers and researchers in Sweden keep their inventions under the teacher's exemption. The practical rule for a company in any of these countries is the same: do not rely on the default. A written assignment signed at hiring, a disclosure process that captures inventions as they happen, and, where the law requires it, a compensation policy are what make the company's ownership hold up in due diligence. This is general information, not advice on a specific contract.

Yes, for every founder, employee and contractor who might contribute to an invention, and before they start work. An invention assignment agreement transfers ownership of inventions made in the course of the work from the person to the company. Without one, the default in the United States is that the inventor owns the invention and the company at best holds a right to use it, and every other jurisdiction has gaps of its own: a UK employee's invention outside their normal duties, a US contractor's invention (work-for-hire covers copyright, not patents), a co-founder's pre-incorporation idea. Investors and acquirers ask for these agreements first in due diligence, and a missing one from a person who has since left is one of the hardest problems to fix.

What a good one contains: a present-tense assignment ("hereby assigns", not "agrees to assign", the wording distinction at the heart of the Stanford v. Roche litigation); a confidentiality obligation; a duty to disclose inventions promptly and cooperate with patent filings, including signing documents after leaving; a schedule of prior inventions the person is carving out; and, where local law demands it, carve-outs for inventions made on the person's own time with their own resources (California Labor Code section 2870 and similar statutes) and a compensation mechanism (Germany, Sweden, the UK's section 40). For founders, sign a founder IP assignment at incorporation covering everything created before the company existed; for contractors, put the assignment in the consulting agreement, since without it they own what they build. Store the signed agreements with the patent files: a portfolio register is only as good as its chain of title. See also Who owns a patent when an employee invents it?

Only if your previous employer or university does not own it, and that depends on what you signed and when you conceived it. Check three things. First, the invention assignment clause in your old employment agreement: most assign inventions made during employment that relate to the employer's business or used its resources, and some include a trailing clause claiming inventions conceived within six or twelve months after leaving; trailing clauses are enforceable in some jurisdictions and not others (California, for example, limits them). Second, conception date: if you conceived the invention after leaving and without using confidential information from the old job, it is generally yours, but you will need to prove the date, so document it. Third, the statutory rules: in the UK, section 39 of the Patents Act 1977 gives the employer only inventions made in the course of your duties; in Germany, service inventions belong to the employer once claimed; in the US the contract governs almost everything.

Universities are a separate case. Most US, UK and German universities claim inventions made by staff, and often by funded students, under their IP policies, and US inventions made with federal funding fall under the Bayh-Dole Act, which gives the university the right to take title. The usual route for a spinout is a licence or assignment from the technology transfer office in exchange for equity or royalties, negotiated before the company files anything. Sweden is the notable exception: under the teacher's exemption, university teachers and researchers own their own inventions, which is why Swedish spinouts often file directly. Whatever the situation, do not file in the company's name and hope: a patent later found to belong to someone else is a due diligence failure that investors treat as fatal. Get the release, licence or written confirmation first, then file.

The person who created it, unless they assigned it to the company in writing. For contractors, this surprises founders most: the US work-for-hire doctrine applies to copyright, not patents, and even for copyright it only covers contractors in narrow circumstances, so a freelance engineer who designs a novel mechanism owns the invention and the code unless the consulting agreement says otherwise. Paying the invoice buys the deliverable, not the intellectual property in it. The fix is an assignment clause in every consulting agreement before work starts, plus an obligation to sign confirmatory assignments later, since a contractor who has moved on has little incentive to help.

For a departing co-founder, the question is what was assigned to the company at incorporation and what the founder agreement says. If everything created before and during the company's life was assigned in a founder IP assignment and the person is still bound by it, the company keeps the IP and the founder keeps whatever vested equity they earned. If no assignment was signed, the departing co-founder still owns their share of the inventions they conceived. In the United States, joint owners of a patent may each use and license it without the consent of, or accounting to, the others (35 U.S.C. 262), so a departing co-founder could license your core patent to a competitor. In the UK, co-owners cannot license without the others' consent, which leads instead to deadlock. Both outcomes are worse than a signed assignment. If a co-founder is leaving and nothing was signed, negotiate the assignment as part of the separation agreement, while there is still something to trade. See also Do I need an invention assignment agreement?