Yoga philosophy is one of the six major orthodox schools of Hinduism, though it is only at the end of the first millennium CE that Yoga is mentioned as a separate school of thought in Indian texts, distinct from Samkhya. Ancient, medieval and most modern literature often refers to Yoga-philosophy simply as Yoga. A systematic collection of ideas of Yoga is found in the Yoga Sutras of Patanjali, a key text of Yoga which has influenced all other schools of Indian philosophy.