This book focuses on ambiguity in Troilus and Criseyde, one of Geoffrey Chaucer’s (1343?-1400) representative works. It examines systematically how and why ambiguity is likely to arise. After reviewing previous scholarship on ambiguity in Chaucer, the author proposes a new theoretical framework, «double prism structure», incorporating the most recent findings in the area of semantics, pragmatics, and cognitive linguistics together with medieval rhetoric and allegory. Using this framework the book examines ambiguity due to textual domains, interpersonal domains and linguistic domains. Ambiguity in Chaucer has not been studied in sufficient detail so far. The work opens new vistas for the study of the phenomenon.