Superb commentary

The date of origin of the Upanishads is unclear as they were initially oral teachings. This excellent translation gives them in their simple glory. The beauty and excellence of this edition is the commentary by Juan Mascaro, one who had penetrated the mystery of Brahman and these teachings. It is from his commentary that the deeper aspects of the timeless wisdom emerges.
For a further metaphysical treatment look for the book by Rene Guenon.