Just as applied linguistics (AL) may be said to be an emerging discipline, so too is one of its sub-fields, second language acquisition (SLA). The parallelism may not be surprising; after all, a difference of only about twenty years separates the points at which the two were identified as autonomous fields of inquiry. Then, too, the two share central defining concepts. AL draws on multidisciplinary theoretical and empirical perspectives to address real-world issues and problems in which language is central (Brumfit 1997). SLA draws on multidisciplinary theoretical and empirical perspectives to address the specific issue of how people acquire a second language and the specific problem of why everyone does not do so successfully. Furthermore, the two share something else: At this juncture in the evolution of AL and SLA, both are grappling with fundamental definitional issues, ones even extending to the nature of language itself. (See Larsen-Freeman 1997a for how this is true of AL.) Should AL and SLA deal successfully with these challenges, both will have much to contribute in the decade to come. Should they instead succumb to internecine feuding and fragmentation, the future will not be as bright.