The FAA’s main concern about Unmanned Aerial Systems (UAS) operations in the National Airspace System (NAS) is safety. It is critical that these aircraft do not endanger other users on the NAS or compromise the safety of persons or property on the ground.
Recreational use of the NAS is covered by AC 91-57 which generally limits operations for aircraft weighing less than 55 lbs. to below 400 feet above ground level, away from airports and air traffic (5 miles). Operations are further limited to line of sight flying (restricting FPV without a spotter), and away from crowds.
From my buddy Chuck at the FAA (September 2014)
Here is the guidance the FAA follows concerning UAV’s. Look at Volume 16. This volume will reference any additional information in the reference sections of each chapter.