A law allowing Cubans to travel abroad without special exit visas took effect on the communist-ruled island on Monday for the first time in half a century.
According to the statute published in the Official Gazette, Cubans can now travel abroad without an exit permit or a foreign invitation provided they have a valid passport.
The reform was anxiously awaited by Cubans eager to travel after enduring painful restrictions since the Cold War era.
Many Cubans have long been separated from relatives living in exile. About one in six Cuban nationals lives abroad.
The law, which came into effect at midnight (5am GMT), is one of the most far-reaching reforms introduced by President Raul Castro since he took over from his ailing brother Fidel in July 2006.
First announced last October, the measure does away with the reviled exit visas that have kept most Cubans from ever traveling abroad.
The visas, and invitation letters from a host, cost up to $200 in a country where the average monthly salary is less than $20.
Rights groups slammed the previous system for impeding Cubans' basic freedom of movement.
Raul Castro's government has ended several unpopular restrictions since 2006. Cubans can now stay in hotels geared to international tourism, sign cell phone contracts and buy electrical appliances. The new system also has allowed Cubans to buy and sell cars and private homes.
But the change taking effect on Monday - Raul Castro's most dramatic to date - could be a stunning wake-up call to the United States, since it has the potential to set off a bilateral migration crisis.
Under a policy dating to the Cold War, the United States still grants any Cuban who reaches US soil legal residency on request. No such US policy exists for nationals of any other country.
With the US economy weak and the election cycle just over, the United States has not been planning for a potential influx of thousands of new Cuban immigrants arriving, legally, by sea and by air.
But is Raul for real?
Dissidents however such as Berta Soler, leader of the opposition movement known as Ladies in White, have expressed skepticism over the measure.
"The immigration reform is no different from all the others," she said. "There will always be some filter. In the end, the government will choose who can or cannot exit the country."
But she said she would be willing to test the law. Referring to the decision of the European Parliament in 2005 to give Ladies in White a human rights award named after the late Soviet dissident and rights champion Andrei Sakharov, she said she would like to go to Strasbourg to collect it.
"Let's see if the European Parliament can organize for us an award presentation ceremony," said Soler.
Dissident blogger Yoani Sanchez said that, along with many other Cubans, she "hesitated between hope and scepticism."
"The migratory reform reflects more the wishes of the government than the desires of people," Sanchez said in a tweet.
The cost of a passport has been doubled to $100, a prohibitive sum for most Cubans without access to hard currency.
Those who can often earn such funds in the tourist trade, while others have remittances sent from relatives living abroad.
Despite travel restrictions in place since the 1960s, Cubans have emigrated illegally in droves, often using rickety boats to embark on dangerous sea voyages to reach nearby Florida.
Around two million Cubans have left the country in the last half century. About a million Cubans and Cuban-Americans live in the US state of Florida alone. The population of the island stands at 11.2 million.