The Upanishads are a collection of ancient Sanskrit philosophical texts that contain some of the central philosophical ideas of Hinduism, some of which are shared with Buddhism, Jainism, and Sikhism.They are among the most important literature in the history of Indian philosophy, religions and culture and talk about metaphysics, ontology, teleology, axiology (ethics and aesthetics), soteriology and the philosophy of the self. The Upanishads played an important role in the development of spiritual ideas in ancient India, and they marked a transition from Vedic ritualism to new ideas and institutions.Early Upanishads are considered by Hindus as part of their scriptures (śruti) that discuss the nature of ultimate reality (brahman) and the character of and path to spiritual liberation (mokṣa or mukti). The Upanishads are commonly referred to as Vedānta, variously interpreted to mean either the “last chapters, parts of the Veda” or “the object, the highest purpose of the Veda”. The concepts of Brahman (ultimate reality) and Ātman (soul, self) are central ideas in all of the Upanishads, and “know your Ātman” is their thematic focus. The Upanishads are the foundation of Hindu philosophical thought and its diverse traditions. Of the Vedic corpus, they alone are widely known, and the central ideas of the Upanishads are at the spiritual core of Hindus. More than 200 Upanishads are known, of which the first dozen or so are the oldest and most important and are referred to as the principal or main (mukhya) Upanishads.The mukhya Upanishads are found mostly in the concluding part of the Brahmanas and Aranyakas[15] and were, for centuries, memorized by each generation and passed down orally. The early Upanishads all predate the Common Era, five[note 3] of them in all likelihood pre-Buddhist (6th century BCE),down to the Maurya period.Of the remainder, 95 Upanishads are part of the Muktika canon, composed from about the last centuries of 1st-millennium BCE through about 15th-century CE.New Upanishads, beyond the 108 in the Muktika canon, continued to be composed through the early modern and modern era, though often dealing with subjects which are unconnected to the Vedas.