Kanji were originally created by the Chinese and introduced to Japan in 4th century A.D. Prior to this, the Japanese had no written language. They borrowed the Chinese characters, but associated their spoken language to them. Because of this, Chinese language kanji and Japanese language kanji are often quite different in meaning and pronunciation. The Chinese pronunciation is often called the on reading, white the Japanese pronunciation is the kun reading.
Unlike the kana, Kanji are not phonetic. Instead they are ideograms, which means each character embodies a specific meaning.
In 1945, the Japanese Ministry of Education developed a list called the Toyo kanji - a list of 1,850 characters meant to include all kanji needed for written communication. The list was renamed the Joyo kanji in 1981. At that time, it was also increased to 1,945 characters. The first 996 Joyo kanji are called the Kyoiku kanji or "educational characters". The Kyoiku kanji are taught in grades 1-6 in Japanese schools. Knowledge of the Joyo kanji enables one to read Japanese newspapers, most street signs, and other important day-to-day written Japanese.