This book is the first to explore how much of knowledge based on research on spoken languages needs to be refined in the light of the growing field of sign linguistics. Drawing upon a broad cross-linguistic perspective, the contributors focus on topics of general theoretical interest: linearity and arbitrariness principles, definition of units and levels of analysis, expression of grammatical categories, semantic relations, and cohesion mechanisms. The book is of interest to language typologists, theoretical and descriptive linguists, scholars in the fields of semiotics, anthropology, gesture studies, and cognitive sciences at large.