Mr Castro, 89, told a party congress that he is handing over the leadership to a younger generation "full of passion and anti-imperialist spirit".
His successor will be voted in at the end of the four-day congress.
Although Mr Castro has not endorsed a successor, it is widely believed the party leadership will pass to Miguel Díaz-Canel, who took over as the island's president in 2018.
When you think about it, Castro is one of the few remaining of his kind. Certainly, there were various people and groups who got power, be it through revolution or electoralism, for the left throughout Latin and South America from the 1950s to the 1980s, before The Pink Tide. Unfortunately, most of them are now dead, either of old age or assassination.
The fact that Castro has lived this long and got to see his country prosper is impressive. About the only other person I can think of who is still alive from that group and time frame is Daniel Ortega in Nicaragua.
well said, absolutely. I'm glad he hand picked from the sounds of it a much younger person he trusts to fill the job. That's what's up.