Liberation of the Atma, through the practice of Yoga, is the goal of many Hindu schools of philosophy.
Yoga is a broad subject but the Patanjali system presented here is based on Sankhya's darshan (philosophy).
This book on Raja-Yoga consists of two parts. The first is based on lectures of the author in New York. 
The second part consists of translations and commentary of a selection of Patanjali's Sutras.