The Principal Upanishads in Their Traditional Order

First in the standard sequence, the Isha Upanishad is only eighteen verses and forms the closing chapter of the Shukla Yajurveda itself. It sets the opening idea of the whole path: the world is pervaded by one divine reality, and it should be enjoyed through renunciation rather than grasping.

Second in the sequence and attached to the Sama Veda, it begins with a student asking what power moves the mind, speech, breath and senses. Its answer is that Brahman is the reality behind all perception, and its story of the gods humbled after a victory shows how that reality escapes being treated as an object.

Third in the sequence, in the Black Yajur Veda, it tells of the boy Nachiketas, who refuses every worldly gift offered by Yama, the lord of death, and insists on learning what happens after death. Yama teaches that the self is never born and never dies and is known through a stilled mind rather than through argument.

Fourth in the sequence and belonging to the Atharva Veda, it is organized as six questions that students bring to the sage Pippalada after a year of study. The answers range from the origin of created beings and the vital breaths to meditation on Om and the destination of a person at death.

Fifth in the sequence and attached to the Atharva Veda, it divides knowledge into a lower kind, covering the Vedas and ritual, and a higher kind that grasps the imperishable directly. Its image of two birds on one tree contrasts the self that experiences with the self that only witnesses.

Sixth in the sequence and the shortest of the principal Upanishads at twelve verses. It reads the syllable Om through four states of the self: waking, dreaming, deep sleep and turiya, the fourth, which is none of these. Gaudapada's commentary on it is the earliest systematic statement of Advaita Vedanta.

Seventh in the sequence and part of the Taittiriya school of the Yajur Veda, it falls into three chapters called vallis. Its second chapter describes five sheaths covering the self, from food up to bliss, and its third records Bhrigu returning to his father again and again with a better answer about brahman.

Eighth in the sequence and embedded in the Rig Veda, it opens with a creation account in which the self alone existed and brought forth the worlds and their guardian deities. It closes with the teaching that consciousness is Brahman, the formula prajnanam brahma that later Vedanta counts among the four great sayings.

Ninth in the sequence, attached to the Sama Veda, and one of the oldest and longest of the principal Upanishads. In its sixth chapter Uddalaka Aruni teaches his son Svetaketu with analogies such as a banyan seed and salt in water, ending in the refrain tat tvam asi, that thou art.

Tenth in the sequence and the longest, generally reckoned the oldest on linguistic grounds, attached to the White Yajur Veda. It is built from dialogues, including Yajnavalkya at King Janaka's court and his teaching to Maitreyi, and it describes the self by negation, neti neti, not this, not that.

Eleventh in the sequence and the first of the three beyond the classical ten, it is widely read as the first Upanishad to teach a personal creator deity, identified with Rudra-Shiva. It rejects proposed first causes such as time, nature and chance, and teaches that this deity is known through devotion as well as meditation.