Shrouded in secrecy, the five-yearly gatherings have marked key events in the party's tumultuous 68-year reign over China and remain a source of intrigue today.
Here are some congresses that have shaped modern China:
The party held its first Congress in 1921 at secret meetings in and around Shanghai. The conclave formally established the aims and charter of the fledgling Communist Party, which included a young Mao Zedong.
The seventh Congress convened at the tail end of the Sino-Japanese war in 1945, at the Communists' stronghold in Yanan, a dusty village in the northern province of Shaanxi. Mao emerged as supreme leader and his "thought" was enshrined as the cornerstone of Party ideology.
In 1969, the ninth Congress met at the peak of the Cultural Revolution, a decade of chaos and near-civil war unleashed by Mao in 1966 to shore up his power base. Mao named army Marshal Lin Biao as his successor and more than 80 percent of the party's Central Committee were fired. Two years later, Lin died in a mysterious plane crash in Mongolia after being suspected of plotting Mao's assassination.
At the 16th Congress in 2002, the party formally allowed private entrepreneurs to become party members, capitalism having previously been officially frowned upon despite the market reforms begun in the late 1970s.
Despite not being members of the wider 25-person Politburo at the time, Xi and Li Keqiang were promoted straight into the then nine-man elite Politburo Standing Committee at the 17th Congress in 2007, marking them out as rising political stars among the so-called fifth generation of leaders.
Xi's two immediate predecessors, Hu Jintao and Jiang Zemin, had their theories inserted into the party constitution at the congresses of 2007 and 2002, respectively, but without having their names directly mentioned, unlike Mao and Deng.
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