the upanishads
The Sanskrit word “Upanishad” in its literal definition means “to sit down near”. In ancient India the Upanishads represented secret teachings reserved for those who sat at the feet of their guru. These texts full of wisdom (whose authors are not known) are also referred to as Vedānta, meaning either the “last chapters of the Veda” or “the highest purpose of the Vedas”. While the main parts of the Vedas contain mostly descriptions of rituals and prayers, the Upanishads are focusing on the realization of the Ultimate – the Knowledge of the Self.
The Muktika Canon lists 108 Upanishads, of which ten are widely considered as the Principal Upanishads.

Morning at Walchensee, © Mahendra Myshkin
These are:
Isha – The Self is the Source of Everything
केन उपनिषद् Kena – From Where Does Everything Arise
कठ उपनिषद् Katha – Nachiketa encounters Death
मुण्डकोपनिषद् Mundaka – Truth alone prevails, not unreality
माण्डूक्योपनिषद् Mandukya – The Four States of Consciousness
तैत्तिरीयोपनिषद् Taittiriya – Bhrigu Learns about Brahman
Aitareya
छान्दोग्योपनिषद् Chhandogya – Satyakama Takes Care of the Cows
Brihadaranyaka