This collected volume combines firmly-grounded theoretical perspectives with historical empirical data from different West Iberian languages (Portuguese, Galician, Asturleonese and Spanish) to deepen our understanding of linguistic divergence in typologically related languages. It is divided into four sections: nominal, verbal and clausal domains, negation and polarity. While varied in their theoretical approach, contributions all serve to examine different aspects of the overarching issue of divergence and how current theoretical frameworks help us understand what factors can account for the actuation changes in West Iberian languages. The book closes with a reflection on various findings about divergence(s), underscoring the importance of incorporating West Iberian languages in revisiting long-standing issues and broadening the empirical evidence available for ongoing research on linguistic theories of language change.