“Drone Sightings and Close Encounters: Analysis” represents the result of a comprehensive and detailed analysis of incidents involving unmanned aircraft and manned aircraft in the U.S. National Airspace System. We have collected records of 921 incidents involving drones and manned aircraft in the national airspace, dating from December 17, 2013 to September 12, 2015. We have organized these reports into two categories: Sightings, incidents in which a pilot or an air traffic controller spotted a drone flying within or near the flight paths of manned aircraft though not posing an immediate threat of collision, and Close Encounters, where a manned aircraft came close enough to a drone that it met the Federal Aviation Administration’s definition of a “near midair collision” or close enough that there was a possible danger of collision, even if an exact drone-to-aircraft distance was not reported. By these criteria, 35.5 percent of the incidents were Close Encounters, and 64.5 percent were Sightings. We found that over 90 percent of all incidents occurred above 400 feet, the maximum altitude at which drones are allowed to fly. A majority of the total incidents occurred within five miles of an airport (which is also prohibited airspace for all drones, regardless of the altitude at which they are flying). Incidents within five miles of airports occurred at lower altitudes than incidents beyond five miles of an airport. Our findings indicate that incidents largely occur in areas where manned air traffic density is high and where drone use is prohibited. We counted 158 incidents in which a drone came within 200 feet or less of a manned aircraft (two-thirds of all Close Encounters in which a concrete drone-to-aircraft proximity is given), 51 incidents in which the proximity was 50 feet or less, and 28 incidents in which a pilot maneuvered to avoid a collision with a drone. One hundred and sixteen of the Close Encounters involved multiengine jet aircraft, 90 of which were commercial aircraft (the majority of which have the capacity to carry 50 or more passengers). We also counted 38 Close Encounter incidents involving helicopters. The reports do not always clearly identify the type of drone involved in incidents, but of the 340 drones that were identified in the reports, 246 were multirotors (i.e. quadcopters, hexacopters, etc.) and 76 were fixed-wing. The locations with the highest number of incidents were large metropolitan areas. Two-thirds of incidents happened between 10 a.m. and 6 p.m., local time.