The idea is that, just as in life, not everything is completely black or white. The two energies compliment, and cannot exist, without each other.
Mentions of the yin yang concept can be found in the I Ching and in forms of Chinese medicine. The symbol is very popular today and is used by many as an expression of their beliefs, as well as a mere decorative image.
Yin Yang Tree Tote Bag £19.98
Yin Yang Wolves Tote Bag £19.98