In a recent comment on Shards leisha asked what differentiates raja yoga from other forms of yoga. My answer is really too long to fit in a comment, so I'm creating this post.
Yoga, in general, means union. It is often taken to mean union with God. Others, who don't focus their beliefs on a personal God, see it as union between the individual consciousness and Universal Consciousness. Madame Blavatsky illustrated it as
the dew drop slipping into the shining sea
In the the realm of the individual, yoga can be the end of the walls between the normal states of consciousness of waking, sleeping, and dreaming.
To imitate Mr. Obvious for a moment, everyone isn't the same. We all have different temperaments and interests. We all have individual talents. We all have areas of expertise. With our individual differences, the same path to expanding awareness wouldn't be suitable for all of us. The creators of yoga have taken these differences and created different yogas to cater to their basic thrust.
They placed people into four broad categories - those who do, those who feel, those who think, and those who experience. Jung's four functions are comparable - sensation, thinking, feeling, and intuition. For each category, they developed a yoga whose emphasis catered to that category's strengths - karma yoga, bhakti yoga, jnana yoga, and raja yoga. Karma yoga and bhakti yoga are especially suited for us as we go about our daily lives as members of economic society. Jnana yoga and raja yoga are especially suited to us when we have time without outside obligations.
As with people, the four yogas are not completely separate categories. They all embody the same steps, which have been codified in Patanjali's Yoga Sutras and the Bhagavad Gita. These steps are yama and niyama (basically purifying processes), introversion, posture, energy control, concentration, meditation, and samadhi, but with different emphases.
Karma yoga is the yoga of work. For the karma yogi, the fruits of work are dedicated to God. One is not working to primarily to attain a goal, but because it is in his nature to act. As Krishna tells Arjuna
To action alone hast thou a right and never at all to its fruits; let not the fruits of action be thy motive; neither let there be in thee any attachment to inaction
Karma yoga is a yoga suitable for all of us. Don't let it's accessibility fool you, though. Just as the rules of backgammon are simple, but mastery of the game is the work of years, so is being able to work without attachment to success the work of years, if not a lifetime.
The process of learning to act without attachment to the outcome of our work gradually purifies the mind from attachments and leaves it ready to experience what is, rather than what we wish to be.
Bhakti yoga is the yoga of love. In Hindu philosophy, deity is conceived of in two ways - with form and without form. All that exists is thus an embodiment of the infinite. In bhakti yoga we emphasize one aspect of deity, such as Christ in Christianity or Krishna in Hinduism. The devotion to our conception of diety, the active love that bhakti demands, cleanses ones mind and heart of attachments and selfishness. We are gradually weaned from our more destructive beliefs, and thus our more destructive emotions.
Jnana yoga is the yoga of philosophy. The goal of jnana yoga is the removal of ignorance. The ignorance meant is not what we usually mean when we say someone is ignorant. The ignorance meant is the inability to discriminate between the real and the unreal, between the temporal and the eternal. As in all yoga, the goal is to step outside of time to experience what we can only describe as the infinite. A great deal of intellectual effort may be spent in pursuit of this goal, but the purpose of the intellectual effort is to remove the small ignorances that disguise the great ignorance. The intellect functions in the realm of form, the world of creation. It is not able to apprehend reality. An example may be seen in the koan in Zen Buddhism. When we work a koan, intellectuality finally gives up, breaks down, and we exerience satori. so it is with jnana yoga. The process of discrimination between the real and the unreal eventually leads the intellect to give up, break down, and the real is experienced.
Raja yoga is the yoga of consciousness. Patanjali defines yoga as the hindering of the modifications of the mind. The goal of raja yoga is to stop the thought process so that one can see what underlies it. A traditional metaphor sees the mind as a lake reflecting the Reality. Thoughts are waves and disturbances on the lake, that when calmed, allow the lake to clearly reflect Reality as a mirror reflects one's face without distortion. When we are successful, we have a sudden moment of illumination in which Paul's
For now we see in a glass darkly, but then face to face
becomes a living reality. Meditation is raja yoga's primary tool, with the preceding limbs of yoga serving to ease the process of meditation. Raja yoga is largely a purification process. In a way, the other yogas are specializations of raja yoga to suit individuals with different temperaments.