1. Introduction; 2. The Neurobiological Basis of Shabd Yoga; 3. The History of Nad and Shabd Yoga; 4. The Sufi Emphasis on the Sound Current; 5. The Sant and Sikh Practice of Shabd and Nam; 6. The Radhasoami Tradition; 7. The Sound Current Tradition in the West; 8. Paul Twitchell and Eckankar; 9. The Sound Current Tradition in Other Religions; 10. Conclusion.