The Upanishads are eternal principles. The power of eternal principles is unlimited. The Isavasya Upanishad is a reservoir of such power. As the first words of this Upanishad are IsaVasyam idham sarvam - it is named the Isavasya Upanishad or the Isa Upanishad. This Upanishad of 18 mantras wonderfully explains the rulership and pervasiveness of Brahman. It talks about matters such as discrimination in indulging in sensual pleasures and the necessity of renunciation. Guidance is also given on the life-oriented approach of karma yoga, the balance of knowledge and karma in life and the benefits of imbibing these principles. The Upanishad concludes with humble prayers. A complex and involved subject like Isavasya Upanishad cannot be taken up for study unless there is constant guidance from a Spiritual Guru. Ordinary people like us who are not specially initiated in the field of Vedanta, can at best prattle what could be gathered from the works of Rishis, Seers, Gurus, Swamis, Yogis and the specially initiated learned men in the field of Vedanta. That is exactly what I have attempted with the fervent hope that people like me can read and get an overall view of what this Upanishad is teaching us.