There are four Mahavakyas, or great statements in the Upanishads, which have a profound significance as pointers to Reality. They are:
Prajnanam Brahma - Consciousness is Brahman;
Aham Brahmasmi - I am Brahman:
Tat Tvam Asi - That Thou Art;
Ayam Atma Brahma - This Self is Brahman.
The Aitareya Upanishad is one of the older, “primary” Upanishads commented upon by Adi Shankara. It is a Mukhya Upanishad, associated with the Rigveda. It figures as number 8 in the Muktika canon of 108 Upanishads.
The Aitareya Upanishad is a short prose text in three chapters and contains 33 verses in total. It comprises 4-6 [...]
Here are some articles exploring the wisdom of Upanishads
The Essence of Upanishads
That Thou Art
Introduction to Katha Upanishad
Summary of Isa Upanishad
Dialog between Gargi and Yajnavalkya
Dialog between Maitreyi and Yajnavalkya
All this is verily Brahman
The Universe as a Sacrificial Horse
Madhu-Vidya - The Honey Doctrine
Brahman can not be known
Shown below are links to the Translations of all 108 Upanishads in Hinduism.
Adhyatma • Advaya Taraka • Aitareya • Aksha Malika • Akshi • Amrita Bindu • Amrita Nada • Annapurna • Aruni • Atharvasikha • Atharvasiras • [...]
The older Upanishads are associated with Vedic Charanas (Shakhas or schools). The Aitareya Upanishad with the Shakala shakha, the Kauśītāki Upanishad with the Bashakala shakha; the Chāndogya Upanishad with the Kauthuma shakha, the Kena Upanishad, and the Jaiminiya Upanishad Brahmana, with the Jaiminiya shakha; the Kaṭha Upanishad with the Caraka-Katha shakha, the Taittirīya and Śvetāśvatara [...]
Due to their mystical nature and intense philosophical bent that does away with all ritual and completely embraces principals of One Brahman and the inner Atman, the Upanishads have a universal feel that has led to their explication in numerous manners, giving birth to the three schools of Vedanta.
Vedantin philosopher Adi Shankara summed up all [...]
Different Upanishads are formally affiliated with the four Vedas (Rigveda, Yajurveda, Samaveda and Atharvaveda). The Upanishads were transmitted orally by the schools of Vedic recitation sakhas. The longest and oldest Upanishad are the Bṛhadāraṇyaka and the Chāndogya.