This book aims to address a gap in the existing literature on the relationship between vagueness and ambiguity, as well as on their differences and similarities, both in synchrony and diachrony, and taking into consideration their relation to language use. The book is divided into two parts, which address specific and broader research questions from different perspectives. The former part examines the differences between ambiguity and vagueness from a bird-eye perspective, with a particular focus on their respective functions and roles in language change. It also presents innovative linguistic resources and tools for the study of these phenomena. The second part contains case studies on vagueness and ambiguity in language change and use. It considers different strategies and languages, including English, French, German, Italian, Medieval Latin, and Old Italian. The readership for this volume is broad, encompassing scholars in a range of disciplines, including pragmatics, spoken discourse, conversation analysis, discourse genres (political, commercial, notarial discourse), corpus studies, language change, pragmaticalization, and language typology.