Beginning December 21, 2015, the FAA will require all drones ("SUA" in FAA terminology) weighing between 0.55 and 55 pounds to be registered before operating outdoors. Failure to register can result in stiff penalties, which can include fines of up to $27,000 or, where criminal liability has been found, a fine of up to $250,000 and up to three years in jail. What this new requirement means for the hobbyist or consumer is that all but the smallest nano-scale quadcopters will need to be registered to be flown outdoors. A very slight exception will made for owners who have personally flown their own aircraft outdoors before December 21st that allows deferred registration of the particular aircraft until February 19th. But this exception comes with so many caveats the takeaway should be, register your drone before you fly outdoors to avoid falling afoul of the FAA or local law enforcement.
Registration will cost $5 and must be renewed every three years. The registration process won't open until December 21; however, you can start the ball rolling today by reading the downloadable documentation at the FAA website. Early registrants who complete their application before January 20, 2016, will see their $5 fee refunded. Once successfully registered, you will receive a unique identification number that must be displayed somewhere accessible, without the use of tools (but not necessarily external), on the drone—inside the battery compartment will probably be ideal, in most cases. The FAA is keen to stress that this number is not the same as an "N-number" or "tail number." Rather, it is a unique code that ties a particular drone to its owner. If you have a collection of several drones, the same number can be applied to each.

The recommended location for your registration number, on the drone itself, is inside the battery compartment.
Since the number pairs with the owner, and not the aircraft, it should be removed if you sell your drone or give it away. The new owner will then need to apply for their own registration number if they do not already have one.
After December 21, registration can be initiated online through the FAA website, or via snail mail. At this time, only non-commercial drones in the 0.55- to 55-pound weight range can be registered online. Commercial operators and hobbyists with aircraft weighing more than 55 pounds must still register the old-fashioned way, through the mail. In these cases, different fees and conditions may apply.
For more information regarding registration and safe flying practices, a great place to start is the official FAQ on the FAA website. Registration applies to users in the US. For operators in other countries, please check with your local authorities or RC clubs in your area to discover what regulations apply.
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