The regional Persian dialects had already developed when the written modern Persian (Dari Persian), devised on the basis of the Arabic alphabetical system, emerged during the second half of the 2nd century A.H. Since then, very valuable Persian literary, historical and scientific works have been written in Dari Persian. Thus Persian regional dialects and the written modern Persian developed continuously and steadily side by side throughout the Persian speaking regions in Iran as well as the neighboring countries. However, during the last two centuries, alongside the two developments, a third form of Persian has appeared, i.e. the standard Persian dialect, mainly in two forms; that is, the slow, detailed vs. the rapid shortened and scrambled spoken versions. In this paper, the writer investigates and describes the nature of the development of the integrated Persian language varieties, as mentioned above.