Within the vast forest of Upanishadic literature, a small group of texts has long been treated as the principal guides to the nature of reality and the Self. Classical Vedānta especially highlights ten as *mukhya* (principal): Īśa, Kena, Kaṭha, Praśna, Muṇḍaka, Māṇḍūkya, Taittirīya, Aitareya, Chāndogya, and Bṛhadāraṇyaka. Alongside these, several others—such as Śvetāśvatara, Kauṣītaki, and Maitrāyaṇi—are also often counted among the major Upanishads, bringing the total in some lists to around thirteen. These texts are closely linked to the four Vedas, being embedded in or associated with their Saṁhitā, Brāhmaṇa, or Āraṇyaka layers, and thus are regarded as core *śruti*, or revealed scripture, for Vedānta.

Their authority is not merely a matter of age, though antiquity is significant; they are among the earliest Upanishads and thus preserve some of the most foundational reflections on ātman and brahman. What especially sets them apart is the intense commentarial attention they received from the great Vedāntic teachers, including Śaṅkara and other major philosophers such as Rāmānuja and Madhva. Because these thinkers chose these texts for systematic exposition, the principal Upanishads became the common ground on which differing schools of Vedānta debated the meaning of Self, world, and ultimate reality. Over time, this shared focus gave them a pan-sectarian status: even when interpretations diverge sharply, the scriptural base remains largely the same.

The content of these Upanishads justifies the esteem in which they are held. Bṛhadāraṇyaka and Chāndogya, among the oldest and most extensive, articulate sweeping visions of brahman and ātman, including teachings such as “neti neti” and “tat tvam asi.” Texts like Taittirīya and Aitareya probe the structure of human experience and cosmology, while Kaṭha and Praśna cast philosophical inquiry in the form of profound dialogues and questions about death, prāṇa, and liberation. Muṇḍaka and Māṇḍūkya, though differing greatly in length, both sharpen the distinction between higher and lower knowledge and analyze consciousness through the symbol of om and the states of waking, dream, deep sleep, and the “fourth.” Īśa and Kena, concise yet dense, explore the relation between action and knowledge and the mysterious source “by whom” all faculties operate.

The additional principal Upanishads extend and color this core vision without departing from it. Śvetāśvatara brings a more explicitly devotional and theistic tone into Vedāntic reflection, integrating yoga and the idea of a personal Lord into the contemplation of brahman. Kauṣītaki emphasizes the supremacy of prāṇa and the journey of the soul, while Maitrāyaṇi elaborates themes of meditation and yoga as vehicles for realizing the Self. Taken together, these texts form a kind of spiritual canon within the broader Vedic revelation: ancient, deeply probed by generations of commentators, and rich enough in doctrine that almost every major Vedāntic idea—about brahman, ātman, karma, rebirth, and mokṣa—can be traced back to their verses.