The Synthesis of Yoga is Sri Aurobindo's principle work on yoga, comparing the methods of the various schools of traditional yoga, and providing the comprehensive way for following the true path to Divine consciousness. It is the primary work on Integral Yoga, the system of yoga that Sri Aurobindo developed.
The book originally appeared in serial form in Arya, published between 1914 and 1921.
Synthesis on Yoga is divided into four parts: the Yoga of Divine Works, of Integral Knowledge, of Divine Love, and of Self Perfection. The first three correspond to the three-fold yoga of the Bhagavad Gita (i.e. karma-, jnana-, and bhakti-yoga), while the last (incomplete) section gives Sri Aurobindo's own development and synthesis of these three paths.
Sri Aurobindo revised the text of the book during three distinct periods. These are: In the 1920s, mostly minor corrections to certain chapters; a full-scale revision during or around 1932, with a view to publishing The Synthesis as a book; and during the early 1940s, further work on the later chapters of Part I, as well as beginning two new chapters, which he apparently intended to add to this part, but which he abandoned before completion. During the later part of the 1940s, Sri Aurobindo lightly revised the entire first part of the Synthesis while preparing it for publication.
In all, some chapters were extensively revised, others had only minor revision, and some have not been revised at all. In 1972 The Synthesis of Yoga was published as Volumes 20 and 21 of the Sri Aurobindo Birth Centenary Library (SABCL); a popular edition that was reprinted many times.
The fifth, 1999 edition, includes some material and revisions not previously published.
Complete on-line version of The Synthesis of Yoga
Selections from The Synthesis of Yoga
http://intyoga.online.fr/soy.htm The Synthesis of Yoga] and [http://intyoga.online.fr/soy_pn.htm History of Revision and Publishing]