Language is social because the motivation to communicate is contingent on the presence of social conspecifics. This thesis studies vocal learning in two social species, humans (Homo sapiens sapiens) and an oscine songbird, the zebra finch (Taeniopygia guttata). Using both behavioral and neuroanatomical data, Chapter 2 of this thesis argues that both the evolution and the development of vocal learning were triggered by the evolution of gated links between subcortical social motivation and cortical learning devices. Chapters 3 and 4 study human vocal learning in the socially motivated contexts in which human infants typically learn language. Chapter 3 studies early phonological learning within a social reinforcement paradigm wherein specific features of the interaction between mothers and infants guide the learning and production of new distributional information. Chapter 4 looks at the effects of changing maternal motivations on maternal behavior, and their subsequent facilitatory effects on infant vocal learning. Chapter 5 suggests that motivation derived from early interactions with social conspecifics drives vocal development in young zebra finches. Overall, this thesis provides evidence that vocal learning is shaped by social interaction and argues for a consideration social motivation as a control parameter in vocal learning.