In this presentation, I will provide an overview of research findings on heritage language (HL) sound systems, with a focus on areas of convergence and divergence among heritage speakers, native speakers who continue to be dominant in the language, and second language learners who started acquiring the language later in life. Drawing on data from a wide range of HLs, I will address global aspects (e.g., accent, intelligibility) as well as more fine-grained aspects of the HL sound system, in connection with variables previously studied as predictors of heritage speakers' behavior (e.g., linguistic features, demographic background, input, methodology). Several recurring themes will be discussed (including intermediate patterning, a higher level of performance in perception than production, and individual variability), and I will also point out a number of remaining questions in this area.