Patanjali, an ancient Vedic sage, who codified the Yogic Science of Raja Yoga, from vedic scriptures like the Upanishads and other ancient vedic scriptures. The Sutras or 'Threads' (similiar to 'sutchers' in english) total over 200 verses. In these threads the whole yogic science is expounded. They are written in sanskrit so naturally translation into english always vary.
A triad of sutras (2nd, 3rd, and 4th) expound the essential function of yoga. They are as follows
2nd sutra - yogash chitta vritti nirodha
(yoga is the settling of the thoughts/waves/modification/modes/aggitations/ of the mind)
3rd sutra - tada drasthuh svarupe vasthanam
(Then the seer exists by itself as the self)
4th sutra - vritti sarupyam itaratra
(at other times the seer identifies with the
thoughts/waves/modifications/modes/aggitations/ of the mind)
Essentially, yoga is about settling and working with you mind. When you settle your mind you realize your true nature and Reality (capital "R"). When you identify with your mind then you are unaware of your true self, hence: the human condition (pain and suffering exist).
Pretty practical, huh?
Below are a list of resources that have translated the Sutras:
- An Interpretive Translation by Swami Venkatesananda (includes audio for some sutras/verses)
- The Theosophy Library version translated by Raghavan Narasimhan Iyer