This is from an online article I found:
"U.S. citizens are barred from traveling to Cuba without government permission under a U.S. trade embargo imposed half a century ago (1959) that can only be lifted by Congress."
Still, the article also went on to say:
"Just over 98,000 U.S. citizens visited Cuba in 2012..."
"As well as allowing Cuban Americans to travel to Cuba freely, Obama authorized licenses for "purposeful" travel to more than 250 Cuba travel agents and allowed more airports to provide charter service between the two countries.
The program, which began in 2011 and requires annual renewal of permission to bring groups to Cuba, allows for educational and cultural travel. The regulations require detailed itineraries of each traveling group."