Though it is technically legal for Americans to visit Cuba (it was ruled as non-constitutional to ban travel to any location), it is not legal to spend money there. Because of this, travel to Cuba is essentially considered illegal and it can be difficult to book travel there if originating from the United States. Violating this law could result in civil penalties and even criminal prosecution. However, the law has several notable exceptions.

Journalists and affiliated personnel: This is strictly for those asked by their employers to go on assignment in Cuba.

Educational programs: There are a variety of these. “Cuba Education Tours”  is an organization that will put together a trip for groups of eight or more. San Francisco’s Global Exchange puts together research tours and has sent tens of thousands of Americans to Cuba. Geographic Expeditions also puts together tours of Cuba as well as Elder Hostel. This may be the easiest route to plan a trip to Cuba, since some of the arrangements are taken care of, but many operators are not currently planning tours to Cuba in hopes that Obama may soon lift the Cuba travel restriction.

Some organizations arrange humanitarian project or religious excursions to Cuba; volunteering for one of these may result in a visit.  See:
fundacionamistad.org
friendshipforce.org
thecajm.org

Professional business: You may be granted permission to visit if there is a conference there, related to your line of work. A Hemingway conference is taking place in Havana in June 2009.

To visit Cuba, traveler must apply for a license (which entails mailing a request letter to the Dept. of the Treasury) and apply for a visa. Details are available here; scroll down to “Applying for…” Click here for Visa information. Cuba Travels U.S. can be helpful for making arrangements. Bear in mind that as this is legally sensitive, many operators, whether educational or humanitarian or otherwise, have vaccilating policies for Cuba travel, based on the present political climate, so offerings may cease and restrictions may change at any time.