Language included in the National Defense Authorization Act (NDAA) for Fiscal Year 2018 grants explicit authority to the Federal Aviation Administration (FAA) to require registration of civilian small unmanned aircrafts, or "model aircrafts." President Donald Trump signed the legislation earlier today.
In May, a ruling by the DC Court of Appeals struck down the FAA's previous attempt to require owners of model aircraft operated for recreational purposes to register with the agency. The court found that the "Registration Rule" directly violated section 336(a) of the FAA Modernization and Reform Act, which prohibits the FAA from "promulgat[ing] any rule or regulation regarding a model aircraft."
Section 1092(d) of the NDAA authorizes the FAA to require such registration. The Conference Report accompanying the NDAA notes that "the conferees believe that registration of unmanned aircraft is consistent with the long-standing requirement for registration of aircraft . . . and is necessary to promote safety and security among all current and future users of the NAS." The Registration Rule is restored effective immediately.
The text of the NDAA can be found here.