The "Bayän al Adyan" (the Exposition of Religions) of Abu 1-Ma'ali Muhammad b. 'Ubayd Allah: Translation, Introduction and Notes. The Bayn al-Adyan is the. earliest Persian work which we have on religions in general and one of the earliest Muslin works on this subject. It was written in 485 A. H. (1092 A. D. ). The translation is based on 'Abbäs Iqbäl's edition, Teheran, 1934, with some additions which I found lacking from the text when comparing it with the original ls. The introduction contains a general study of the text. The notes are an attempt to elucidate and clarify this concise text. They are meant to be a full commentary on it. They are of two kinds : (a) these written on non-Muslim religions, (b) those written on Muslim sects. In (a), I have attempted to give some aspects of the Muslim knowledge of these religions, as presented by the early Muslim authors. When discussing (b) I have attempted to use books written by members of each particular seat, but in the absence of such books other available sources had to be used. Modern studies have been referred to in both sections when necessary. Beside this, I have prepared for publication a treatise on Zaydi theology entitled, "Misbah ul-Ulum fi Ma'rifat al. Hayy al-Qayyum" written by a Zaydi called Ahmad b. al-Hasan ar-Rassas (d. 600 or 656 A. H. ) by collating six Mss. of it, preserved in the British Museum. I have also produced a chapter on the rise of Kharijism from a book entitled "al-Kashf wa 'l-Bayan" written by an Ibadi Khariji called Abu Sa'id a1-Qal/hati. This work is a unique M.S. in the British Museum. The chapter referred to above is given in an abbreviated English translation because the text is corrupt in some places. As far as I know, this is the first time an account of Khärijism, written by a Khariji, has been published.