Protective function: The prior user right protects persons who have developed and used an invention before the filing date of a patent.

Validity of the patent: The patent remains valid despite the prior user right; only a personal exception in favor of the prior user is created.

Ownership of the invention: The prior user must have mastered the invention technically; mere ideas or plans are not sufficient.

Good faith: The prior user must not know or suspect that another person has applied for the same invention.

Genuine use: In addition to ownership of the invention, serious acts of use or concrete steps toward commercialization are required.

No publicity required: Secret use is sufficient; if prior use is public, the patent itself would be invalid.

Material scope: The prior user may continue to use the invention in the form in which it was used previously; quantities may increase, but new patented features may not be added.

Modifications: Changes are permitted as long as they do not fall under the patent claims.

Territorial restriction: The prior user's right only applies in the country in which the prior use actually took place.

Customers protected: The prior user's customers and distribution channels are also privileged and cannot be sued by the patent holder.