The Gàn dialect group is one of the major Sinitic language families of China. It was identified later than most of the other major Chinese dialect complexes and did not play a role in the philological work of earlier scholars such as Bernhard Karlgren and his epigones. Indeed, it was only in the final decades of the last century that enough detailed data on the group became available to support meaningful comparative research. Three book-length works of great importance that appeared in the 1990’s were the Kè-Gàn fāngyán diàochá bàogào of Lǐ Rúlóng and Song-Hing Chang (1992), Les Dialectes Gan (1993) by Laurent Sagart, and the Kè-Gàn fāngyán bǐjiào yánjiù of Liú Lúnxīn (1999). With these major contributions in hand, Sinological linguists at last began to grasp the full nature and extent of the Gàn family. Since the advent the new century, many more articles and several book-length works have appeared, dealing both with individual Gàn varieties and with entire groups of these dialects. Indeed, our ever-growing corpus of Gàn material is now quite impressive. However, to the best of our knowledge, as of this writing no comparative phonological reconstruction covering the entire family has appeared in print. It is accordingly the primary goal of the present work to remedy this deficiency. To wit, we propose to reconstruct a Common Gàn phonological system and then to demonstrate how this reconstruction can be used as a tool for the study of lexical, taxonomic, and historical problems in comparative Gàn. In order to undertake a comparative reconstruction, one must begin by deciding what to compare. In the case of Gàn, this proves to be a complex issue, for no cogent classificatory scheme for the family has so far been proposed. Indeed, the late Professor Jerry Norman once remarked that it is easier to say what Gàn is not than to say what it is. In confronting this conundrum, our initial approach will be to use in our comparative work only dialects that are universally recognized as Gàn, and to set aside for the nonce any whose assignment to the group is problematic or disputed. Then, once our common phonological system has been reconstructed, we shall return to the problem of taxonomy and, by comparing our new common system with others posited for contiguous dialect families, we shall attempt a delineation of the Gàn family as a whole. Finally, when these tasks have been completed, we shall be in a position to propound a set of guidelines for testing the affiliations of those dialects whose taxonomy is currently in question. The first chapter of this monograph introduces the dialects to be compared and outlines methodological issues and procedures. The second, third, and fourth deal with the reconstruction of the Common Gàn syllable initials, syllable finals, and tones respectively. The fifth chapter is devoted to a set of experimental lexical studies, in which our reconstructed phonological system is brought to bear on seventy-eight salient words in the common Gàn lexicon. The sixth and final chapter outlines the demographic history of the Gàn-speaking area, identifies the major lexical strata in Common Gàn, and correlates these demographic and stratigraphic findings. It then presents a full historical hypothesis regarding the formation of the Gàn family and, as mentioned above, addresses directly the problems of taxonomy and classification. A list of References follows Chapter Six. The Appendix lists all cognate sets used in the reconstructions. A short Index to the text of Chapters I-VI is included at the end.