This chapter discusses a common reality in many cases of multilingualism: heritage speakers, or unbalanced bilinguals, simultaneous or sequential, who shifted early in childhood from one language (their heritage language) to their dominant language (the language of their speech community). To demonstrate the relevance of heritage linguistics to the study of linguistic competence more broadly defined, we consider the reorganization of morphosyntactic feature systems, the reanalysis of atypical argument structure, the attrition and simplification in syntax. All these phenomena implicate diverging trajectories and outcomes in the development of heritage language. The chapter also discusses more general concepts central to linguistic inquiry, in particular, complexity and native speaker competence. By opening the chapter with a discussion of bilingualism in Menominee as described in the 1920s by Bloomfield, the author shows that the phenomenon of heritage language is much older than the current term.