Of the many Yoga paths leading to God or the Supreme Reality, four are more commonly known. These are Karma Yoga or the Path of Selfless Services, Bhakti Yoga or the Path of Devotion, Raja Yoga or the Path of Mind Control and Jnana Yoga or the Path of Intellectual Analysis. Even among these, Raja Yoga is popularly known as just 'Yoga'; and similarly, Jnana Yoga is known as just 'Vedanta'.
Of the four paths, again, Raja Yoga is the one which is the most scientifically organized. It is also known as 'Ashtanga Yoga' or the 'Yoga of Eight Steps', each step or rung leading in logical progression to the next one. Raja Yoga is the ladder connecting our phenomenal existence with the Great Noumenon and we have to ascend this ladder step by step with great care and circumspection. No step can be ignored or bypassed except at one's own peril. Progress is assured provided the rules of the game are adhered to. And violation of the rules is bound to cause its own peril. Such is Raja Yoga propounded by that ancient sage Patanjali in the form of Sutras or terse aphorisms collectively known as 'Yoga Darshana'.
'Yoga Darshana' is a difficult text, difficult to understand straightaway even by those with a good knowledge of Sanskrit. So Maharshi Vyasa wrote a commentary on 'Yoga Darshana', and subsequently, Vachaspati Mishra Ji, wrote a more elaborate Gloss explaining the full meaning of Sage Vyasa's Commentary. 
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So we brought out in 1982 a series of discourses given in English by Swami Krishnanandaji on Patanjali's Yoga Sutras under the title, 'Yoga as a Universal Science'. It was very well received by the public thirsting for a knowledge of the deeper implications of the great science of Yoga. We have great pleasure now to bring out this companion volume on the same subject of 'Ashtanga Yoga' by Swami Chidanandaji. The present volume contains the edited version of a series of lectures given by Sri Swamiji to the Third Batch of trainees who underwent the Three Months' Course run by the Yoga-Vedanta Forest Academy of the Divine Life Society. In the hands of Swami Chidanandaji, the Yoga Darshan comes to new life as a vibrant, living guide to spiritual practice. And Swami Ji has delved deep into all the most essential aspects of Yoga Sadhana, and in doing so, has beautifully maintained logical sequence. And the whole volume reflects his earnest desire and longing that spiritual seekers should put to use this marvelous science of Yoga for furthering their spiritual advancement. [Publisher's Preface]