Kena Upanishad—literally “by whom?”—is a short but profound mukhya Upanishad, probably composed in the early first millennium BCE and attached to the Sāma Veda. Framed as teacher–student dialogues, it probes the ultimate cause behind speech, mind and the senses, showing that Brahman is the imperceptible ground beyond intellect and language. Key themes include the limits of reason, the inner controller (ātman/Brahman), the primacy of direct spiritual insight, and ethical humility before the transcendent. Adi Śaṅkara and later Vedantins drew on it heavily. Today Kena’s inquiry into consciousness, the source of action and knowledge, speaks to seekers, philosophers and scientists alike—inviting a contemplative reorientation beyond ego, habit and mere information.