Before 1997, Hong Kong was a British colony. When China resumed control of wealthy Hong Kong, it was agreed to continue the greater freedoms the people of Hong Kong enjoyed compared to mainland Chinese.
Having one part of the country where there is significantly greater political freedom represents a challenge to the Chinese authorities. In Hong Kong there is a freer press, there are opposition parties and political protest is legal. Half of the government is non-communist although the Chief Executive is approved by the CPC (currently CY Leung).
The CPC describes its policy towards Hong Kong as 'One Country, Two Systems'. Most of the political freedoms agreed in 1997 are still in place but the Chinese authorities remain concerned about continued demands for full political freedom.
In August 2014 the Chinese government in Beijing ruled that candidates for the election of a new chief exectuive in 2017 would be from a list pre-approved by the CPC.
This led to widespread protests in Hong Kong. Led by activist groups including Occupy Central, Scholarism, and the Hong Kong Federation of Students, tens of thousands of people took to the streets in protest. Many carried umbrellas as a sign of passive, non-violent resistence and as a result the protests became known as the 'Umbrella Revolution'.
After failed talks with Chinese authorities, some violent clashes and growing opposition from local people fed up with the disruption, the protest camps were cleared by mid-December. However some protestors have said they will continue campaigning for democracy.