A dialect continuum or dialect chain is a series of language varieties spoken across some geographical area such that neighboring varieties are mutually intelligible, but the differences accumulate over distance so that widely separated varieties may not be. This is a typical occurrence with widely spread languages and language families around the world, when these languages did not spread recently. Some prominent examples include the Indo-Aryan languages across large parts of India, varieties of Arabic across north Africa and southwest Asia, the Turkic languages, the varieties of Chinese, and parts of the Romance, Germanic and Slavic families in Europe. Terms used in older literature include dialect area (Leonard Bloomfield) and L-complex (Charles F. Hockett).
Dialect continua typically occur in long-settled agrarian populations, as innovations spread from their various points of origin as waves. In this situation, hierarchical classifications of varieties are impractical. Instead, dialectologists map variation of various language features across a dialect continuum, drawing lines called isoglosses between areas that differ with respect to some feature.