The unity principle, also known as the principle of "one
application for one invention", means that one patent
application shall be limited to one invention. The unity principle
is a fundamental principle for patent applications, and in addition
to state or regional patent laws in the world, PCT (Patent
Cooperation Treaty) defines this principle.
It becomes a universal principle for a number of reasons. The
first is economic consideration. The patent examination
organization requires the applicants to pay certain fees to
maintain the normal operation of the organization and enable it to
complete the search and examination of patent applications.
Typically, the fee paid by an applicant is based on the number of
patent applications. If the number of inventions included in a
patent application is not limited, an applicant may only pay the
fee for a patent application, but request to examine a number of
inventions, leading to heavy economic burden of the
