De Wikivoyage :
A tourist visa card (visa de tarjeta del turista) is necessary for travellers from most nations. This visa, which is really little more than a piece of paper on which you list your vital statistics, costs between 15-25 CUC (or 15-25 Euro), depending on where purchased. It can be purchased at the Airport in Cuba on arrival, however it should be noted that many airlines will require a valid tourist visa card before boarding flights. It is usually valid for 30 days and can be extended once for another 30 days at any immigration office in Cuba (for 25 CUC) - beyond this you would need a flight out of Cuba within the extended visa period. Canadians are the exception, getting 90 days on arrival and can apply for a 90 day extension. Your passport needs to be valid at least six months past the end of your planned return.
Mas alguns países não precisam disso:
Citizens of Antigua and Barbuda (28 days), Barbados (28 days), Benin, Bosnia and Herzegovina, CIS (except Ukraine and Uzbekistan), Dominica, Grenada (60 days), Liechtenstein (90 days), Macedonia, Malaysia (90 days), Mongolia, Montenegro (90 days), Namibia, Singapore, Slovakia, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, Serbia (90 days), Turkmenistan who can stay 30 days without visa.
Também vale a pena notar que é diferente se você é um cidadão americano ... com mais detalhes sobre o mesmo link do Wikivoyage.