A Raja (sometimes spelled Rajah) is a king, or princely ruler. The female equivalent is Rani (sometimes spelled Ranee). Raja comes from the Sanskrit word rājan and has a long history in the Indian subcontinent. Some rulers would give themselves the title as a means to increase prestige among their subjects. The word maharaja connotes a raja who has conquered other rajas, thus becoming a great ruler. Variants include Rana, Rao, Raol Rawal, and Rawat.

In South India, the title of the Hindu emperor of Vijayanagar, instead of raja, was called raya. Raja is used in India to distinguish a Hindu king from a Muslim Nawab or Shah, and still is commonly used in India. Elsewhere it does not have the same religious suggestion.

The ruler of the Malaysian state of Perlis is to this day known as the Raja of Perlis. The White Rajahs of Sarawak in Borneo were James Brooke and his dynasty.

Raja is also one of the four major Yogic paths of Hinduism. Raja Yoga involves psycho-physical meditational techniques to attain experience of the truth and finally achieve liberation described in Hindu thought to be moksha.