This article presents linguistic innovations which are typical of both Courland and Salaca Livonian and are also known in the neighbouring Estonian dialect areas. These innovative features are phonological, morphological, and morphosyntactic. The features are present mainly in western and southwestern Estonia, but also more specifically in areas close to the current western border between Estonia and Latvia. This article discusses the nature and chronology of these linguistic features, taking into account their distribution. Broadly spread common features can be mostly explained as inherent innovations of western Finnic when they are not shown to be caused by contacts with Germanic or Baltic languages. Features which are spread in the immediate vicinity of the former Livonian language area can be classified as a Livonian substrate in sub-dialects of western and insular Estonian.