The Aitareya Upanishad is one of the older and ancient Upanishadas annotated by Shankara. It is a main or `Mukhya` Upanishad affiliated with Rigveda. The Aitareya Upanishad is a short prose containing three chapters and thirty-three verses in total. The second book is Aitareya Aranyaka, that is an older Vedic text and comprises three chapters the fourth, fifth and sixth chapters.

The sage or the Rishi who put forward the verses of Aitareya Aranyaka and Aitareya Brahmana is Aitareya Mahidasa who is believed to live for hundred and sixteen years (Chhandogya).

The Aitareya Upanishad depicts the Atman or inner self as the divine creator in its first chapter, while in the second chapter it describes the three births of Atman. The third chapter deals with the qualities of self or Brahaman. It contains the most famous expression of Vedanta "Pragnanam Brahma", which is among the "Mahavakyas`.

Part I:
Chapter I-
The Creation of Virat : In the beginning there was nothing but Atman only, He bethought himself "Let Me now create the worlds." He created the worlds: Ambhah, the world of water bearing clouds; Marichi, the world of solar rays; Mara, the world of mortals; Ap, the world of waters. Heaven was the support for `Yon`. Marichis are the interspace, Mara is the earth and whatever underneath is called Ap.

The Atman then wanted to create the guardian and right from the water he took a lump, which he gave shape into a person. The supreme lord then brooded over him and his mouth was separated with an egg. From the mouth organ of speech generated and gradually fire developed as the controller of the organ. Thus various other organs like organs of breath and sight, ears, skin, hairs, heart, mind all generated along with their controlling deities like air, sun, space, Varuna etc. From the hairs plants and trees developed. Finally the virile member was separated out. From the virile member semen was separated as the means of generation and water was created as the controlling deity.

Chapter II-
Cosmic Powers in the Human Body: The deities, thus created, fell into the great ocean. The supreme lord subjected the virile person to hunger and thirst and instructed him to find an abode where food can be eaten. He brought the deities a cow but that was not enough for them. He brought them a horse but that was also not enough for them. He brought them a person and deities were pacified. Then the deities could enter their respective abodes.

The fire deity became the organ of speech and entered the mouth. Air was the ruler of breath and entered the nostrils. The sun became sight and entered the eyes; the quarters of space became hearing and entered the ears. Plants and trees became hairs and entered the skin. The moon became mind and entered the heart. Death entered the naval. Water became semen and entered the potent member.

Hunger and thirst also sought an abode for them. The Atman made them co-sharers with the deities.

Chapter III-
The Embodiment of the Supreme Self : After the creation of the world and the world guardians, God created food for them. He brooded over waters and the water was condensed to create the food. The food wanted to flee away and he grasped it with speech but was failure. Then he tried to grasp it with breath, skin or ear but was unable to do it. So one is never satisfied when he utters the word food or smells it, touch it or hears or thinks about the food. Finally he could grasp the food with `Apana` situated on the naval region. The grasper of the food was `Vayu`, air or `Prana`. So Vayu sits on the food.

Then the question that arose into the mind of Supreme Lord is who was he and where he belongs to in his own creation? He entered through a door or cleft called `Vidriti` and assigned himself three positions. He was born as `Jiva` and realized that unison of the elements with him. Therefore the Supreme Lord is called as `Idandra` or directly as `Indra`.

Part II:
Chapter I-
The Three Births of the Self- The person is at first a germ in the semen, which is vigor drawn from all the limbs. Man bears the self within the self. When a man pours the semen into a woman the first birth of the soul is assured. The semen becomes the part of the woman and does not hurt her. She nourishes the semen as her limb and the part of man becomes the part of woman. As the woman nourishes the embryo she also needs to be nourished. She also nourishes the child after it is born. This is the second birth. Thus a man is born through his child. When he accomplishes his jobs and ready to leave the world, his other self is ready to substitute his duties. Thus, departure of a man is considered as the third birth.

About this the Rishi said, "While still lying in the womb, I came to know all the births of the gods. A hundred strongholds, as if made of iron, confined me, yet I burst through them all swiftly, like a hawk." Vamadeva was a wise man who spoke even while he was in the womb.

Thus, man is empowered with knowledge and becomes one with the Supreme Self , obtaining all desires in the heavenly world and become immortal through the rebirth of the Atman.

Part III-
Chapter I-
Concerning the Self- The question comes into mind that who is this self whom we worship? Is he the same by whom one sees form, hear sound and taste the sweet or unsweet. The consciousness or `Prajnanam` is in different forms of knowledge, wisdom, retentive power of mind, sense, steadfastness, thoughtfulness, sorrow, memory, concepts, purpose, desire or longing. As Rishi says- `He is Brahman, He is Indra, He is Prajapati; He is all these gods; He is the five great elements-earth, air, akasa, water, light; He is all these small creatures and the others which are mixed; He is the origin-those born of an egg, of a womb, of sweat and of a sprout; He is horses, cows, human beings, elephants-whatever breathes here, whether moving on legs or flying in the air or unmoving. All this is guided by Consciousness and is supported by Consciousness. The basis is Consciousness. Consciousness is Brahman.` He thus realizes oneness with the Consciousness and becomes immortal.

End of Aitareya Upanishad- The Peace Chant :
The great piece of religion, theology, philosophy and mysticism, Upanishada therefore stands as an emblem of spirituality and piousness. In the last chapter of the Aitareya Upanishada, the Sage utters the peace chant-

"May my speech be fixed in my mind, may my mind be fixed in my speech! O self-luminous Brahman, be manifest to me. O mind and speech, may you bring me the meaning of the Vedas! May what I study from the Vedas not leave me! I shall unite day and night through this study. I shall think of the right; I shall speak the right. May Brahman protect me, may Brahman protect the teacher! May Brahman protect me, may Brahman protect the teacher!

Om. Peace! Peace! Peace!"