'The Tao described in words is not the
real Tao,
Words cannot describe it.
Nameless it is the source of creation;
Named it is the mother of all things.'
Lao Tzu, Tao Teh Ching
Tao gave birth to One; One to Two;
Two to Three;
Three to the Ten Thousand Things.
Lao Tzu
Philosophical taoism can trace its roots to the I Ching, most commonly translated as the Book of Changes. Besides expounding the Taoist idea of a universe which is constantly changing, the I Ching was used a a source of divination of future events, or perhaps more accurately possible future events. The books was traditionally held to be written by King Wen and his son Duke Chou in 1150 BCE.
The prime apologist for philosophical taoism was Lao Tzu. It is not clear if Lao Tzu was an actual person or not. The name means Old Sage and may well be a name used to represent the collective writers of several Taoist texts. If he lived it was in the 5th century BCE. Lao Tzu is know for three major works on Taoism. The most famous by far is the Tao Teh Ching. Two of his other well know works are the Hua Hu Ching and Wen-Tzu.
Second among the Taoist Sages was Chuang Tzu. He is best know by the book which bears the same title as his name. This work was completed in the 4th century BCE. A more practical exposition of the principals of Taoism is the Art of War by Sun Tzu. In this work Sun Tzu applies the principles of Taoism to military science.
Perhaps the greatest obstacle that westerners face in trying to understand Taoist texts is the fact that we are not Chinese. The Chinese language to the western way of thinking is very ambiguous and prone to many interpretations when translated into English. In my opinion all such efforts are ultimately doomed to failure since the essence of the Chinese way of thought and language can not be rendered into western languages without corrupting the meaning fatally. This can best be illustrated by looking at multiple translations of the Tao Teh Ching into English. When reading these various translations of the first sutra of the the Tao Teh Ching keep in mind that everyone one of them is a translation of exactly the same Chinese text.
For further readings on Taoism visit one of the most comprehensive Taoist web sites I've come cross.