This monograph focuses on dialects of European Portuguese and presents research in diatopic variations of verbal inflection in mainland Portugal. It is based on a corpus compiled from dialectological dissertations and dialectological surveys by Manuel de Paiva Boléo and Luís F. L. Cintra, in which these variations are identified. It subsequently describes their historical development and localizes them aiming to reveal their relation to northern or southern dialects of Portuguese. Finally, it categorizes them as phenomena of a phonetic, morphological or morpho-phonological nature.