In every part of the world, already thousands of years ago, humans have speculated about some kind of life force. In China it is called qi (also spelled chi), in India prana, in ancient Greece pneuma, in Latin spiritus, and in Hebrew ruach. There are hundreds of life energy beliefs, which have many similarities. This encyclopedia presents and explains them all. In the introduction, distant origins of human thought are traced, examining how spiritual beliefs and life force ideas emerged, and how they were developed through time.

Stefan Stenudd is an author and historian of ideas, who researches the thought patterns of myth in general and creation myths in particular. He is also a high-grade instructor of the peaceful and spiritual martial art aikido, since 1972. Aikido, too, evolved from ideas of a life energy.