The Chinese Communist Party's more than 80m-strong membership makes it the biggest political party in the world. Its tight organisation and ruthlessness help explain why it is also still in power.
The party oversees and influences many aspects of people's lives - what they learn at school and watch on TV, even the number of children they are allowed.
It is made up largely of government officials, army officers, farmers, model workers and employees of state-owned companies.
It is unrepresentative of China as a whole. Only a quarter of its members are women, for example. It is also obsessive about control, regularly showing itself capable of great brutality in suppressing dissent or any challenge to its authority.
Joining the party brings significant privileges. Members get access to better information, and many jobs are only open to members. Most significantly in China, where personal relationships are often more important than ability, members get to network with decision-makers influencing their careers, lives or businesses.Pyramid structure
To join, applicants need the backing of existing members and to undergo exhaustive checks and examination by their local party branch. They then face a year's probation, again involving assessments and training.
The party has a pyramid structure resting on millions of local-level party organisations across the country and reaching all the way up to the highest decision-making bodies in Beijing.
In theory, the top of the pyramid is the National Party Congress, which is convened once every five years and brings together more than 2,000 delegates from party organisations across the country.
The congress' main function is to "elect" a central committee of about 200 full members and 150 lower-ranking or "alternate" members", though in fact almost all of these people are approved in advance.
In turn, the central committee's main job is to elect a new politburo and its smaller, standing committee, where real decision-making powers lie.