What are the unique characteristics of sign languages that make them so fascinating? What have recent researchers discovered about them, and what do these findings tell us about human language more generally? This thematic and geographic overview examines more than forty sign languages from around the world. It begins by investigating how sign languages have survived and been transmitted for generations, and then goes on to analyse the common characteristics shared by most sign languages: for example, how the use of the visual system affects grammatical structures. The final section describes the phenomena of language variation and change. Drawing on a wide range of examples, the book explores sign languages both old and young, from British, Italian, Asian and American to Israeli, Al-Sayyid Bedouin, African and Nicaraguan. Written in a clear, readable style, it is the essential reference for students and scholars working in sign language studies and deaf studies.