The Chinese Zodiac is thousands of years old and easily predates its Western counterpart. Even today, millions of believers across the globe consult the Chinese Zodiac regularly.
While Western Astrology is based upon the months of the year, Chinese Astrology is based upon a twelve year lunar cycle. Your sign is determined by the year in which you were born (to be accurate you must use a Chinese calendar). Each sign and those born under it, are represented by one of twelve animals, and are ascribed a set of attributes the Chinese believe comprise the nature of each particular animal.