Only recently has linguistic research recognized sign languages as legitimate human languages with properties analogous to those cataloged for French or Navajo, for example. There are many different sign languages, which can be analyzed on a variety of levels—phonetics, phonology, morphology, syntax, and semantics—in the same way as spoken languages. Yet the recognition that not all of the principles established for spoken languages hold for sign languages has made sign languages a crucial testing ground for linguistic theory. Edited by Susan Fischer and Patricia Siple, this collection is divided into four sections, reflecting the traditional core areas of phonology, morphology, syntax, and semantics. Although most of the contributions consider American Sign Language (ASL), five treat sign languages unrelated to ASL, offering valuable perspectives on sign universals. Since some of these languages or systems are only recently established, they provide a window onto the evolution and growth of sign languages.