Karma yoga , (also known as Buddhi Yoga) or the "discipline of action" is based on the teachings of the Bhagavad Gita, a sacred Sanskrit scripture of Hinduism. Of the four paths to realization, Karma Yoga is the science of achieving perfection in action. Karma Yoga is an intrinsic part of many derivative types of yoga, such as Natya Yoga.
Background
The Bhagavad Gita gives a summary of the Karma Yoga process. The Gita itself is a chapter from the epic known as Mahabharata, wherein a dialogue takes place between the prince Arjuna, and his friend and chariot driver, Lord Krishna, on the brink of a great dynastic war. Their conversation is prompted by Arjuna as he is engulfed by sorrow and misgivings regarding the oncoming battle in which he has friends and relatives on both sides. In reply, Krishna then elucidates upon a number of philosophical yoga systems and practices (including Karma Yoga) by/through which he should indeed continue with the fight on righteous principles
Concept
The word Karma is derived from the Sanskrit Kri, meaning 'to do'. In its most basic sense karma simply means action, and yoga translates to union. Thus Karma yoga literally translates to the path of union through action. However, in Vedantic philosophy the word 'Karma' means both action and the effects of such action. Karma Yoga is described as a way of acting, thinking and willing by which one orients oneself toward realization by acting in accordance with one's duty (dharma) without consideration of personal self-centered desires, likes or dislikes. Acting without being attached to the fruits of one's deeds.
Lord Krishna speaks:
Therefore, without being attached to the fruits of activities, one should act as a matter of duty, for by working without attachment one attains the Supreme.
Krishna then goes on to describe how Arjuna should surrender the fruits of his actions (good or bad) to him, Krishna, (as the Supreme Person or avatara) :
Therefore, O Arjuna, surrendering all your works unto Me, with full knowledge of Me, without desires for profit, with no claims to proprietorship, and free from lethargy, fight.
Krishna explains that work done without expectations, motives, or anticipation of its outcome purifies one's mind and gradually makes an individual fit to see the value of reason. He states that it is not necessary to remain in external solitude, or remain actionless, in order to practice a spiritual life, since the state of action or inaction is primarily determined in the mind.
In order to achieve perfection of life, Krishna explains that it is important to control all mental desires and tendencies to enjoy pleasures of the senses. The practice of Karma Yoga in daily life makes an individual fit through action, meditation and devotion to sharpen his reasoning, develop the intuitive power of acquiring knowledge, and to transcend the mind itself.