The Yoga Sūtras of Patañjali are 196 Indian sūtras (aphorisms) that constitute the foundational text of Rāja yoga. Yoga is one of the six orthodox āstika schools of Hindu philosophy, which, according to the Yogatattva Upanishad, is divided into four forms – Mantrayoga, Layayoga, Hathayoga and Rājayoga – the last of which is the highest (or royal) practice.