The Isha Upanishad belongs to the Shukla Yajurveda and runs to eighteen verses. It opens with the line that all this is pervaded by the Lord, and moves from there to how a person may act and live within that understanding. Its brevity has made it a common place to begin among the principal Upanishads.
✦ Did you know
The Isha Upanishad does not sit at the end of a Veda like the others. It sits inside one — as the fortieth and final chapter of the Shukla Yajurveda's Vajasaneyi Samhita.
Source: Vajasaneyi Samhita, adhyaya 40