Among the Mohammedans Súfíism, or Persian mysticism, is known as _tasawwuf_. The word Sidi is derived from _súf_, meaning "wool." When a little Persian sect at the end of the eighth century A.D. broke away from the orthodox Muslim religion, and struck out on an independent path, they ignored costly robes and worldly ostentation, and clad themselves in a white wool garment. Hence they were known as "wool wearers," or Súfís. Prof. Edward G. Browne[1] gives four theories in regard to the origin of Súfíism, viz.: (1) _Esoteric Doctrine of the Prophet_.(2) _Reaction of the Aryan mind against a Semitic religion_. (3) _Neo-Platonist influence_.(4) _Independent origin_. Neither of the four theories altogether satisfies the learned professor, and very certain it is that the last-mentioned theory is of very little account. Prof. Browne seems in favour of a "spontaneous growth" existing in various forms, under various names throughout the civilised world; but after all this is not very tangible evidence. Moreover, we must bear in mind that the Neo-Platonist philosophers paid a visit to the Persian court in the sixth century A.D., and founded a school there in the reign of Núshír-wan. It is highly probable, therefore, that these seven philosophers, forced to leave their homes through the tyranny of Justinian, who forbade the teaching of philosophy at Athens, should have had considerable influence upon a few of the more thoughtful Persians. We shall now find that this theory is borne out by internal evidence. Let us briefly study the tenets of Neo-Platonism. The Neo-Platonists believed in the Supreme Good as the Source of all things. Self-existent, it generated from itself. Creation was the reflection of its own Being. Nature, therefore, was permeated with God. Matter was essentially non-existent, a temporary and ever-moving shadow for the embodiment of the Divine. The Neo-Platonists believed that by ecstasy and contemplation of the All-Good, man would rise to that Source from whence he came. These points bear directly upon the Súfí teaching. They form a broad outline of the tenets of Súfíism. The Súfís, from temperamental and other causes, elaborated these ideas, gave them a rich and beautiful setting, and, what is all-important, built about them one of the most interesting phases of mystical poetry the world has ever known, and this particular phase may be said to date from the twelfth century A.D.