The origins of Basque dialects, a highly disputed area of research in Basque studies, are examined. The author, the foremost expert on Basque dialects, traces their emergence to medieval times, using: a) the profusion of features common to all dialects: b) the large number of innovations common to all dialects; and c) the fact that the only truly divergent dialects are the western and Souletin ones. In contrast, the three central dialects differ in far fewer and less important respects. The main contribution of Standard Basque and Its Dialects to the scholarly debate about the formation of Basque is that it identifies the nuclei from which the current dialects almost certainly emerged. The book explains the points of view that Basque speakers have upheld concerning their dialects, the formation of provincial standards starting in the eighteenth century, and the launch of Standard Basque in the second half of the twentieth century.