In the past year, regime's Great Fire Wall system restricting foreign content has been raised to keep out Twitter, Facebook and many other sites
Google's retreat from China comes amid an intensifying crackdown on the country's internet that has seen websites blocked, an entire region closed down and self-censorship become increasingly widespread.
In the past 12 months the Great Fire Wall - China's system of restricting foreign content - has been raised to keep out Twitter and Facebook. Many other sites, such as YouTube, were already blocked.
Within China censors stepped up their efforts to limit information available to an increasingly connected nation by expanding lists of taboo subjects, putting pressure on internet service providers (ISPs) and arresting several high-profile journalists and free speech campaigners who refused to toe the line.
The Guardian's Chinese language service, the Weibao, was taken offline without explanation at the end of last year when the site of its translation partner, Yeeyan, was removed by its internet service provider.
Last June the government attempted to install "Green Dam" censorship software in every computer that would deny access to sites with pornographic or politically sensitive content.
The plan was postponed at the last minute after a backlash by Chinese netizens, computer makers and foreign governments, but the authorities are said to be still keen to introduce such a system.
After riots erupted in the far western region of Xinjiang in the summer, the authorities completely shut down the internet in the capital, Urumqi, and restricted mobile phone messaging. Services were only resumed in the past month.
Google, along with other companies that operate within the Great Firewall, must follow the orders of the Communist party propaganda department. Their executives meet with Chinese officials who tell them "which way the wind is blowing" on sensitive topics such as Tibet, Taiwan, Tiananmen and Falun Gong.
Many website operators compile lists of terms that might get them in trouble with the authorities and filter them from their content. Almost nothing is made public, which means there is an invisible line between what is acceptable and prohibited. This results in massive self-censorship.
Criticism of China's actions at the Copenhagen climate summit is thought to be off-limits. At least one website operator flags up even the word "China" because stories about the nation are potentially sensitive.
Google has been criticised by the authorities and sporadic breaks in its Chinese service have been widely seen as a form of temporary punishment for failing to heed the orders of the censors. It faces unfair competition with Baidu, the local rival search engine that is far more compliant.
Censorship was high on the agenda when Barack Obama made his first visit to China in November. In a town hall meeting in Shanghai the US president described himself as a as "a big supporter of non-censorship" and said criticism made him a better president.
"I think that the more freely information flows, the stronger the society becomes, because then citizens of countries around the world can hold their own governments accountable," Obama said. "They can begin to think for themselves."
Many Chinese netizens find ways to "climb the firewall" by using proxies and VPNs to access blocked websites overseas. Some, such as the artist Ai Weiwei, rail against censorship and the sanitised domestic news offerings.
The government has tried to scare off such challenges by imprisoning high-profile campaigners. The Tibetan film-maker Dhongdup Wangchen was recently jailed for six years for a critical documentary about Tibet. Liu Xiaobo was handed an 11-year sentence for instigating a campaign for constitutional reform, including greater freedom of expression. Zhao Lianhai is awaiting trial after using the internet to campaign for justice over the poisoned milk scandal of 2008.
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