The term ‘Yoga’ according to Patanjali’s definition means the ‘final annihilation (nirodha) of all the mental states (citta-vrttis)’ involving the preparatory stages in which the mind has to be habituated to being steadied into particular types of graduated mental states. This was actually practiced in India for a long time before Patanjali lived; and it is very probable that certain philosophical, psychological, and practical doctrines associated with it were also current long before Patanjali. The Yoga doctrines taught by Patanjali are regarded as the highest of all Yogas, Raja Yoga, as distinguished from other types of Yoga practices, such as Hatha Yoga or Mantra Yoga. Of these Hatha Yoga, consists largely a system of bodily exercises for warding off diseases, and making the body fit for calmly bearing all sorts of physical privations and physical strains. Mantra Yoga is a course of meditation on certain mystical syllables which leads to the audition of certain mystical sounds. In the present book an attempt has been made to study the METAPHYSICS OF SAMKHYA-YOGA.