Travelers visiting Cuba are required to hold a valid passport valid for at least 2 months following their travel date, medical insurance, and proof of return tickets. Proof of sufficient funds to support the stay is also required (50 dollars/day).
Visa-free entry for a period upwards of 28 days is granted to citizens of Antigua and Barbuda, Barbados, Belarus, Benin, Bosnia and Herzegovina, Dominica, Grenada, Malaysia, Mongolia, Montenegro, Namibia, North Macedonia, Saint Vincent and the Grenadines, Russia, Saint Kitts and Nevis, Saint Lucia, Serbia and Singapore (Kazakhstan and Kenya are scheduled to soon complete the list).
The remaining majority of international visitors will need to obtain a Tourist Card, Tarjeta del Turista, that grants permission to stay in Cuba for 30 days and can be extended once for a further 30. The card can be obtained via the airline, travel agent or a Cuban mission abroad.
Citizens of the following countries are not eligible for a Tourist Card and will need to apply for a visa: Afghanistan, Bangladesh, Cameroon, Eritrea, Ethiopia, Ghana, Guinea, India, Iran, Iraq, Kenya, Nepal, Nigeria, Pakistan, Philippines, Sierra Leone, Somalia, Sri Lanka, Syria, and Yemen. Admission is refused entirely to Kosovo nationals.
Special regulations apply to citizens of the USA, who (as of 2018) will need to qualify for one of 12 visitor categories in order to be granted an entry visa. The easiest way to enter Cuba for USA citizens under these regulations is to join an excursion organized by a tour operator (these are also available on board cruise ships), that falls into the "people-to-people exchange program" category of the 12 officially approved. Another, slightly more complicated route, is to obtain a license issued by the U.S. Department of Treasury.
Special regulations apply to Cuban-born foreign citizens, who will need to make visa arrangements for a Cuban visa in advance (via a Cuban Embassy), unless they hold a valid Cuban passport.