Although China"s Communist Party exerts huge power and influence over the everyday lives of its citizens, there are several activists who continue to pose major problems for the authorities.
Hu Jia, probably China"s most prominent activist, was sent to prison for three-and-a-half years for writing five articles and giving two interviews.
He has long sought to publicise what he believes are injustices in China concerning the environment, HIV/Aids and human rights. In April, Beijing"s First Intermediate People"s Court interpreted these acts as an attempt to subvert "the state"s political and socialist systems". But human rights groups say the Chinese authorities put the campaigner in prison to silence him ahead of the Olympic Games.
As well as being sent to prison, Mr Hu was deprived of political rights for one year. The state-owned Xinhua news agency reported that Mr Hu wrote articles criticising the Chinese political system, and accepted interviews with foreign journalists.
"Hu spread malicious rumours, libel and instigation in an attempt to subvert the state"s political and socialist systems," it said. Mr Jia suffers from liver disease due to Hepatitis B infection. Amnesty International says the family has been unable to provide him with medicine. He is receiving some medication from prison authorities, but his family are concerned that this may not be adequate.
YE GUOZHU, Activist, in jail
Ye Guozhu was sentenced to four years in jail in 2004 after he tried to organise a demonstration against evictions in Beijing. He was arrested after he applied to stage a 10,000-strong rally in the Chinese capital and was found guilty of disturbing the social order and convicted for "picking quarrels and stirring up trouble".
He had been protesting since his family"s home was knocked down in 2003 to make way for a wave of planned redevelopments ahead of the Olympic Games. He was due to be released on 26 July at the end of his sentence, but Amnesty International has said it is uncertain whether he will be freed.
The group says authorities may use his attempts to challenge his conviction as a pretext to extend his imprisonment beyond the Olympic Games.
He reportedly continues to suffer from health problems, partly as a result of being beaten with electro-shock batons and being subjected to periods of "discipline" in prison, says Amnesty.