Between 5,000 and 10,000 Chinese characters, or kanji, are used in written Japanese. In 1981 in an effort to make it easier to read and write Japanese, the Japanese government introduced the joyo kanji, which includes 1,945 regular characters, plus 166 special characters used only for people's names. All government documents, newspapers, textbooks and other publications for non-specialists use only the these kanji. Writers of other material are free to use whatever kanji they want. Japanese children are required to know all of the joyo kanji by the end of high school but to read specialist publications and ordinary literature, they need to know another two or three thousand kanji.
The word kanji is the Japanese version of the Chinese word hanzi, which means "Han characters". Han refers to the Han Dynasty (206BC - 220AD) and is the name used by the Chinese for themselves.
Whent the Japanese adopted Chinese characters to write the Japanese language they also borrowed many Chinese words. Today about half the vocabulary of Japanese comes from Chinese and Japanese kanji are use to represent both Sino-Japanese words and native Japanese words with the same meaning.