FACTBOX: Cuba's one-party political system

(Reuters) - Cuba's National Assembly is widely expected to name Raul Castro as head of state on Sunday following Fidel Castro's announcement on Tuesday that he is retiring. The following is an outline of Cuba's one-party communist system.

* Cuba is a one-party socialist republic, in which political power is vested solely in the Cuban Communist Party (PCC). The political system is enshrined in the Cuban Constitution approved by a national referendum in 1976. Another referendum in 2002 made socialism "irrevocable."

* The PCC was founded in 1965 by merging various parties and revolutionary groups under Fidel Castro's leadership. All other political parties were banned.

* Until Tuesday, Fidel Castro held the three top political leadership posts on the island: head of state (as president of the Council of State), head of government (as president of Council of Ministers) and first secretary of the party. He has stepped down as president but retains the party post.

* The National Assembly is the Cuban legislature with 614 delegates who are elected every five years. Half of them emerge from municipal and provincial assemblies called People's Power (Poder Popular). Delegates are not required to be members of the party but most are.

* At its first session every five years, the National Assembly approves a slate of 31 members of the Council of State, the highest executive body headed by the president, a first vice president and five second-tier vice presidents.

* On Sunday, the National Assembly is expected to confirm Fidel Castro's brother, Raul Castro, as Cuba's new head of state following the ailing leader's announcement he is retiring.

* Cuban society is organized into "mass organizations" of workers, students, women and farmers. The biggest is a network of neighborhood block committees, known as the Committees for the Defense of the Revolution, whose stated task is to mobilize political support for the government and defend the political system against crime and "counter-revolution." Critics say they facilitate political control over the population.

(Reporting by Anthony Boadle, Editing by Frances Kerry)

(For special coverage from Reuters on Castro's retirement, see: here)