Before switching to the regular solar calendar of the western origin, the Chinese used to follow their own calendar which was based on lunar cycles. So, Chinese astrology is based on the conventional lunar calendar, which has twelve cycles of the moon.
There are twelve different animals in Chinese zodiac. Each zodiac period consists of full moon cycle, from new moon to full moon. Therefore, twelve full lunar cycles are there in a Chinese Zodiac year. However, one animal stands for a whole year. So, a Chinese cycle goes round for twelve years before starting all over again. Unlike in western system, where your zodiac comes around every year, in the Chinese system you can celebrate your zodiac birthday only once in twelve years.
There are several legends associated with the creation of the Chinese calendar. One of them has it that the gods wanted to test which of the animals could reach their position the fastest. So, they asked all of them to compete by swimming through a river. The order of their reaching is reflected in the Chinese zodiac. According to another legend, before leaving earth, Lord Buddha asked the animals to visit him. And when they went to meet...