The Story
In USA, before the 70s, driving a scooter on the street was not something you could see every day. In fact, in many States, there were restrictions on the mopeds where they were prohibited on the streets. However, a man called Serge Seguin was the first to introduce it in 1972. He started to promote it explaining their fuel savings and he went to the congress to try to popularize it. He was successful in making a specific classification for mopeds in more than 30 states. Since they could travel 220 miles with a single tank and they could run at a max speed of 30mph, these small vehicles gain popularity with the 1970 energy crisis and more than 250,000 people already had one by 1977. But when the gasoline price started to go down and the cars started to be built to consume less oil, the moped boom started to vanish.
The Problem:
When you buy a moped, you need to take into account that each state in the USA has its own regulations, so you need to check in your DMV (of the State where you live) to see what are the requirements regarding title registration and license required to drive one. Generally, the regulations to ride a scooter is not strict and you can drive it with your car's license, but you must read and learn what are the restrictions and how to apply for a title and how much it costs. The same applies for the protective gear to wear and the insurance that you need to apply for.
The Solution:
You can check this post that pretty much explains what are the requirements in each state:
http://www.genuinescooters.com/scooter-state-laws.html