Flying ultralights is an exciting and exhilarating sport when done safely.
Ultralights are regulated and defined in Federal Aviation Regulations; FAR Part 103
An Ultralight is a single seat vehicle, weights less than 254 pounds, 155 pounds max empty weight,
carries 5 gallons of fuel or less and is capable of flying as slow as 24 knots and no faster than 55 knots.
if the aircraft has more than 1-seat or exceeds any of the above criteria, It's not an ultralight.
No FAA pilot license or FAA medical exam required to fly an ultralight. The ultralight does not required to be maintained by an FAA certified mechanic.
An ultralight can not be flown over any congested area of a city, town or settlement, or over any open air assembly of persons.
The ultralight can't be used for any commercial purposes.
An ultralight can only be operated during sunrise and sunset unless equipped with anti-collision light extending flight time to twilight periods, 30 minutes before sunrise and 30 minutes after sunset
Even thought the FAA does not require that you have a FAA pilot's license to fly it doesn't mean that you can fly it safely without training. Use common sense for the need of training .
Light Sport Aircraft are used for training.