Evolution of language has evolved at multiple levels - from changes in the cognitive processes by which language is acquired in the individual, to language change by diffusion of acquired linguistic features across populations of individuals, to the emergence of linguistic features over phylogenetic time scales. Evolution of language at each of these levels interacts with that at each other level. This volume is a collection of essays by noted researchers from diverse fields that deals with a broad spectrum of issues in the study of language evolution. The principle topics addressed here include: the genetic and cognitive bases for the phylogenetic emergence of language; several distinct accounts of the underlying cognitive processes by which children learn to acquire language; a critique of the methods employed by historical linguists in the last century; the modeling of language evolution using mathematical and computational techniques; and, discussions on the complexity of language.