Hinduism and Islam are usually considered to be poles apart especially on religious grounds. But in this work, the author has endeavored to demonstrate that in spite of sharp differences between them, they met on religious, commercial, intellectual and political levels both in and outside of India. Although orthodox Hinduism and orthodox Islam could hardly reconcile, it is shown here that they were bound to accommodate each other however, the real fusion took place with the coming to India of a host of Sufis especially the lives and conduct of the left wing mystics of both religions made the two peoples to come closer through bhakti mysticism. Of the many bhakta mystics who strove in this direction, Dr. Hedayetullah made a special study of Kabir (D. 1518) who dedicated his whole life to the achievement of Hindu-Muslim unity on socio-religious levels. So far Kabir has not only been denied his rightful credit as an apostle of Hindu-Muslim unity, but he has also been misunderstood by many. In the present work, he is shown to have gained the place of honor between the two religions as a mediator and a harmonizer. His efforts were crowned with success, the resultant Indo-Islamic culture and civilization is a living proof.