Yoga is the stilling of the mind, as described by Patanjali in the Yoga Sutras, through an ethical, healthy lifestyle and consciousness raising practices which create Self-awareness. The word Yoga comes from the root Yuj, meaning to yoke or join. It is a joining, or uniting, of the individual self with the universal Self. The individual self being our ordinary sense of self identified with our egoic mind, the universal Self being our higher consciousness which is beyond association with individual personality traits and beyond judgment: seeing all as one.
Yoga is the science of Self-realization: a system of practices first codified by the ancient Rishis (seers) in India that recorded their knowledge into the Vedas. Veda means knowledge, and the Vedas are scriptures that were composed between around 1700 and 500 BC. The first Veda that mentioned the word Yoga was the Rig Veda. The Vedas are subdivided into parts. The first three parts are composed of chants and rituals to be undertaken by Brahmin priests as a path of self-sacrifice and worship. The Upanishads are the fourth part of each Veda that discuss methods of meditation and philosophy on the path to Self-realization. The most celebrated of the Upanishads is the Bhagavad Gita, a part of a greater epic called the Mahabarata, written around 500 BC. The Upanishads shift the practice from external ritual and physical sacrifice to an internal practice of dissolution of the ego through the paths of study (Jnana Yoga), work and service (Karma Yoga), worship of God (Bhakti Yoga) and meditation (Raja Yoga).
Living sometime between the 4th and 2nd century BC, the sage Patanjali composed 3 books: the Mahabashya, a treatise on Sanskrit grammer, Patanjalatantra, a medical book on Ayurveda, and the Yoga Sutras (sutras=threads or aphorisms) in which he consolidated the vast body of yoga as had been passed down orally and through the Vedas into a concise treatise on the methods and goals of Yoga. The methods were codified into the Ashtanga or Eight-fold Path, and have been called the path of Raja Yoga, Raja meaning king or supreme. The Yoga Sutras is one of the most important texts for how the science of Yoga is understood in the west.
In the early part of this millennium, the idea that the physical body was a hindrance on the path to enlightenment began to be discarded as Yoga masters began to embrace the body as a means of Self-realization. They saw the body as portal to the inner world and developed techniques to purify and revitalize it, leading to the somatic practices of Hatha Yoga.
In the late 19th century Indian Yoga masters first began to travel and spread the teachings of Yoga to Europe and North America. Swami Vivekananda delivered lectures on Yoga at the 1893 Parliament of Religions in Chicago. Shortly thereafter Paramahansa Yogananda toured America lecturing on Yoga as a path to Self-Realization. In India during the 20s and 30s Sivananda and Krishnamacharya promoted the physical practices of Hatha Yoga. Krishnamacharya passed on his teachings to several people who would then spread the teachings to the West, most notably BKS Iyengar, Sri Pattabhi Jois, Indra Devi, and his son TKV Desikachar. Iyengar became known for his therapeutic, slow style with alignment as a central focus. Sri Pattabhi Jois founded the Ashtanga school of yoga (not to be equated with the Ashtanga 8 fold path of Patanjali) in which practitioners are given a specific series of postures to practice and perfect as they advance in a very strong and physical practice. Indra Devi, one of the first western women to advance the practice, opened a popular yoga studio in Hollywood in 1947. Sivananda was producing hundreds of books on yoga and establishing ashrams and yoga centers internationally.
In the past few decades yoga has become increasingly popular all over the world, with many styles and instructors teaching various aspects of the Yoga path.