For decades, groups based in Miami, Florida have launched literally hundreds of terrorist attacks against the Cuban people and Cuban Nationals. These include bombings, assassinations, and particularly boatloads of weapons sent to Cuba to be used against its citizens. It is estimated that at least 3,478 people have died, and 2,009 have been injured as a direct result of these acts of terrorism. 
The Cuban government, quite reasonably, sought to thwart such attacks. Five Cuban Intelligence officers: Gerardo Hernández, Antonio Guerrero, Ramón Labañino, Fernando González, and René González were dispatched to infiltrate and monitor these Miami-based groups to protect their countrymen. They did succeed in uncovering some of these plots.
On September 12, 1998, these men were arrested and indicted on a charge of Espionage Conspiracy.  They were sentenced to lengthy prison sentences including 17 months in solitary confinement!
Supporters of the Five argue that the trial which indicted the men was fundamentally unfair, that they have been subjected to cruel and unusual punishment and that the prosecution was politically motivated.
Two of the Five, Fernando Gonzalez, and René Gonzalez have been freed, but the other three remain locked up. One of the men, Gerardo Hernandez, faces TWO life sentences plus a fifteen year sentence on top of that.
In this episode of the Global Research News Hour, special guest interviewer Lesley Hughes interviews Gloria La Riva, an organizer with the National Committee to Free the Five (quoted above) and the first of the five to be freed, René González.
President Obama, YES YOU CAN free the Cuban Five!
People wishing to get involved in current and ongoing solidarity efforts to free the Cuban Five, or who merely wish for more background are encouraged to visit the following sites:
There are also two important books on the subject:
Letters of Love and Hope: The Story of the Cuban Five with an Introduction by Alice Walker 
What Lies Across the Water: The Real Story of the Cuban Five by Stephen Kimber