Question: what are the principal upanishads?
Answer: Mukhya Upanishads, also known as Principal Upanishads, are the most ancient and widely studied Upanishads of Hinduism. Composed between 800 BCE to the start of common era, these texts are connected to the Vedic tradition. The most early colonial era Indology listed 10 Upanishads as Mukhya Upanishads.