Under U.S. patent law, more than one inventor may apply for the same patent if each inventor contributed to thinking of the invention (made some contribution to the subject matter of at least one of the claimed inventions) and each was at least aware of the other's work. In fact, if joint inventorship has occurred, a U.S. patent application must be filed in the names of all of the inventors.
Joint inventorship is present when two or more people collaborate in conceiving a claimed invention. Each person must be aware of the contribution of the other and each must contribute to the formation of the solution to a problem that is the invention. Thus, joint inventorship is the process by which parties cooperate to solve a problem and in which each party makes some mental contribution to the final conception of the solution. The entire inventive concept need not occur to each of the joint inventors and they need not physically work on the project together or at the same time. Furthermore, the contributions need not be the same or equal. All that is required is collaboration and contribution to at least one of the claims in a patent application.
Law - Joint Inventorship