Areal variation refers to spatial variants of morphological variables within and between languages. Variation within languages is the topic of dialectology. As dialects of the same language share most of their morphological features, this article evidences, first of all, the differences displayed by dialect variants of a variable. With respect to the variation between languages, in this article, similarities between the languages compared are pointed out. Such similarities may be a consequence of language universals, of common historical origins, of chance convergences, or they may be geographically conditioned, e.g., sprachbund characteristics. An additional aspect in this context is the center-periphery pattern, in the sense that structural similarities may be found at the margins of a linguistic area, regardless of whether or not the languages in question are closely genetically related.