Dialectology (from Greek διάλεκτος, dialektos, "talk, dialect"; and -λογία, -logia) is the scientific study of dialects: subsets of languages. Though in the 19th century a branch of historical linguistics, dialectology is often now considered a sub-field of, or subsumed by, sociolinguistics. It studies variations in language based primarily on geographic distribution and their associated features. Dialectology deals with such topics as divergence of two local dialects from a common ancestor and synchronic variation. Dialectologists are ultimately concerned with grammatical, lexical and phonological features that correspond to regional areas. Thus they usually deal not only with populations that have lived in certain areas for generations, but also with migrant groups that bring their languages to new areas (see language contact). Commonly studied concepts in dialectology include the problem of mutual intelligibility in defining languages and dialects; situations of diglossia, where two dialects are used for different functions; dialect continua including a number of dialects of varying intelligibility; and pluricentrism, where a single language has two or more standard varieties. Hans Kurath and William Labov are among the most prominent researchers in this field. Source: Wikipedia (en)