The I Ching or Book of Changes, is an ancient divination text and considered the oldest of the Chinese literary classics. Written approximately 3000 years ago, it has become one of the most influential books in Chinese history.
Through chance a number is determined, using dice, coins, rice grains, yarrow stalks and even turtle shell cracks and other methods. Today it is even possible to determine these numbers via random number generators on web sites or in mobile apps. The resulting 6 numbers are then turned into a hexagram which can be looked up in the I Ching, similar to scriptures in the Bible.
The text is then consulted to answer questions such as business, health, children, and determining lucky days and to provide guidance for moral decision making as informed by Taoism and Confucianism. These texts or 'scriptures' so to speak, often of a high poetic nature, are accompanied by commentaries to further explain the meaning. In modern days it's become very common for people to hit their I Ching App, punch out a few random numbers and read the resulting text or scripture to determine a particular course of action or decision.
A page of the I Ching
It can be compared to astrology or other types of divination, in which 'luck' or 'fortune' seemingly steered by destiny and/or divine beings determine the outcome and the by the text suggested decision or course of action. Many heads of states, leaders, intellectuals and religious leaders both in the East and West have used it to consult on decisions, or plain curiosity.
Its proper use is debated. While many use it as a sort or oracle, this is not always the case. Sun Tzu for example forbade the use of the I Ching to work out battle strategies, since he felt they needed to be determined by an officer's deeper knowledge and not simply 'luck'. Nevertheless, it is most commonly used as a tool for fortune-telling.