Upanisads are the culmination of Vedic thought and one of the great episodes of the history of the human spirit. Together with the Vedic hymns and the Bhagavaddata, they constitute the sacred texts of Hinduism. A broad body of knowledge that was "heard" by ancient sages and transmitted orally for centuries. They contain dialogues, poems, aphorisms and teachings aimed at identifying the sacred principle and strength that animates everything. The upanisad fascinated Schopenhauer and the romantics.

For Vedic thought, the world as a whole and human life in particular are a perpetual sacrifice, whose fire is breathing. The Sanskrit word upanisad, meaning "correspondence" or "link", has a ritual dimension and a philosophical dimension. Correspondences make sacrifice possible and justify it, while establishing affinities between the different areas of the real and mapping the hidden bonds that make up the warp of the world.

For the first time, a complete translation of the main upanisad from the Sanskrit original is published in Spanish. A careful edition that has taken into account the various interpretations of ancient and modern commentators, and in which sanscritists from different parts of the world have participated.