Who must wear a helmet while riding a motorcycle?

In Maine, all motorcycle operators and passengers under the age of 18 are required to wear helmets while riding. Operators of any age who have held their license for less than one year, or who are riding with a learner's permit, are also required to wear a helmet while riding. If an operator is required to wear a helmet, any passenger they are transporting is also required to wear a helmet, regardless of the age of the passenger.