Traditional and Simplified Chinese
Despite the large differences among Chinese dialects, there is one thing in common for them - they all share the same writing system based on Chinese characters.
In Mainland China a simplified writing system is used, whereas in Hong Kong, Taiwan, and overseas regions traditional Chinese is being used. Since learning Chinese requires years of study, a large percentage of the Chinese population was illiterate. After the Chinese Cultural Revolution, many of the new government leaders decided that the current writing system was too difficult. To make learning easier, they created an alternate character set by modifying traditional characters to make them easier to write.
The simplified writing system differs in two ways from the traditional writing system: (1) a reduction of the number of strokes per character and (2) the reduction of the number of characters in common use (two different characters are now written with the same character).
Traditional Chinese characters are still very widespread, until recently both Hong Kong and Taiwan used traditional characters almost exclusively. More and more publications are using simplified characters, but there are many works available only in traditional Chinese.
Apart from the different writing system, there are also some slight deviations in grammar, vocabulary and styles between the written forms of the language in different Chinese speaking regions. For instance, while it is commonly asserted that both Taiwan and Hong Kong use traditional Chinese characters, one will find considerable variation in their respective character inventories, largely as a result of their different languages. Cantonese, the language spoken in Hong Kong, has many specific characters that are in widespread use locally, but will not be found used in Taiwan. Taiwanese introduces a number of specific characters as well. To get an idea of how divergent this can be, it is estimated that Cantonese employs several thousand special characters that are not widely used outside of Hong Kong and overseas Cantonese-speaking communities.