Patanjali and Yoga is a clear and straihtforward look at the history, development and meaning of yogic thought now proving of such interest to the West. It is not just another book of methods and practices.
Yoga originated in archaic magical means intended to overcome human anguish and suffering, These methods were known long before Patanjali, but Eliade has chosen to focus on the Yoga Sutras of Patanjali, who was the first to write down and codify "classic yoga." Following in Patanjali's path, Indian thinkers have been quick to distinguish true yoga from trances, self-hypnosis and false ecstasies. The many forms and aspects of yogic practice constitute a major part of India's history.
From earliest times, India has concerned itself with what we in the modern West call altered states of consciousness. Yoga allows a release from deterministic conditioning and permits the yogi to release himself into the true, indescribable freedom of liberation. With that release comes the appearance of extraordinary powers baffling to modern scientists and easily confused with "magical" or "occult" powers. Here is a comprehensive introduction to the foundations of yogic thought and practice. [via]