The Yoga Sutras

Patanjali Maharishi (great sage) was an Indian teacher who is credited with composing the small Sanskrit volume of Yoga Sutras from which the modern practice of yoga is derived. He is believed to have lived between 250 B.C.E. and 450 C.E. and is traditionally thought of as the person who gathered and systematized the teachings of meditation and yoga. It is said that desiring to teach yoga to the world, he (pat-) fell from heaven
(-añjali) into the open palms of a woman/earthly world, hence the name Patanjali.

Yoga tradition is much older than the Yoga Sutras. There are references in ancient Vedic works of the Mahabharata, Bhagavad Gita and Yogatattva Upanishad. The Yoga Sutras codifies the royal/Raja or best yoga practices, presenting them as an eight-limbed system (ashta/eight -anga/limbs). The philosophic tradition is related to the Samkhya school.

Patanjali's Yoga Sutras contains 196 aphorisms into 4 chapters (or books/pada)

sutra - literally means a rope or thread that holds things together
aphorism - a concise statement of a principle, a terse formulation of a truth or sentiment and easily memorable

1. Samadhi Pada (51 sutras) Samadhi refers to a blissful state where the yogi is absorbed into Oneness. The author describes yoga and then the nature and the means to attaining samadhi. This chapter contains the famous verse: "Yoga chitta-vritti-nirodha"
Yoga is the cessation of the fluctuations of the mind.

2. Sadhana Pada (55 sutras) Sadhana is the Sanskrit word for "practice" or "discipline". Here the author outlines two forms of Yoga: Kriya Yoga (Action Yoga) and Ashtanga Yoga (Eightfold or Eight limbed Yoga). Kriya Yoga is also expounded in Chapter 3 of the Bhagavad Gita, where Arjuna is encouraged by Krishna to act without attachment to the results or fruit of action and activity. Ashtanga Yoga
describes the eight limbs that together constitute Raja Yoga.

3. Vibhuti Pada (56 sutras) Vibhuti is the Sanskrit word for "power" or "manifestation" which can manifest by the practice of yoga.

4. Kaivalya Pada (34 sutras) Kaivalya as used in the Sutras stands for emancipation, liberation and used interchangeably with moksha (liberation), which is the goal of Yoga. The Kaivalya Pada describes the nature of liberation and the reality of the transcendental self.