Held every five years, party congresses normally are the main political event in a one-party system like Cuba's that brooks no dissent.
The last one in 2011 introduced significant reforms of the island's moribund Soviet-style economy, cracking open the door to small-scale private enterprise and foreign investment.
This one, the Seventh Congress, had raised expectations in Cuba and abroad that it could set the stage for accelerated political and economic changes following a rapprochement with longtime foe the United States.
But Cuban authorities have poured cold water on those hopes, signalling that continuity will be the watchword at the four-day, close-door session involving 1,000 delegates and another 3,500 invited participants.
In contrast with the last party congress, which was preceded by a wide-ranging public debate, this one will be held in secret, with only the state-controlled press allowed to cover the proceedings.