Raja Yoga stems from the ancient text Yoga Sutras by Patanjali. The eight stages of yoga that Patanjali describes are together called Raja Yoga. Raja Yoga is well known for its ethical guidelines of yamas (self-restraints) and niyamas (observances).
The yamas are: ahimsa (non-violence), satya (truth), asteya (non-stealing), bramacharya (moderation) and aparagraha (nonpossessiveness).
The niyamas are: saucha (purity), santosh (contentment), tapas (austerity), swadhyaya (study) and ishvar pranidhana (surrender).
These form the basis for remaining six stages of Raja Yoga: asana, pranayama, pratyahara, dharana, dhyana, and meditation. The ultimate aim is samadhi – merging with universal consciousness. It should be noted that these practices as taught in Raja Yoga are quite advanced, it is not for beginners or intermediate practitioners, but for persons who have already purified themselves to a great degree through Hatha, Karma and Bhakti yogas and awareness meditation techniques.
For an explanation of Raja Yoga and commentary on the Yoga Sutras, see Four Chapters on Freedom by Swami Satyananda.