As stipulated in Executive Order 10096, "The Government shall obtain the entire right, title and interest in and to all inventions made by any Government employee (1) during working hours, or (2) with a contribution by the Government of facilities, equipment, materials, funds, or information, or of time or services of other Government employees on official duty, or (3) which bear a direct relation to or are made in consequence of the official duties of the inventor."
Federal employees, contractors, and students have an obligation to report inventions and are required to assign rights to the Federal government. The form used for reporting employee inventions, called an Employee Invention Report (EIR), can be found here:
Employee Invention Report (EIR)
In some cases, inventions are licensed to companies in the private sector. The NIH shares royalties with inventors in accordance with the NIH Royalty Policy.