Based on a multi-year ethnography in one Spanish-speaking community in New Jersey, this book is a meticulous account of six Mexican families that explores the relationship between siblings’ language use patterns, practices, and ideologies. Combining insights gained from language socialization and heritage language studies within the larger field of sociolinguistics, the book’s findings examine siblings’ sociolinguistic environments and the ways in which these Latino children use and view their multilingual resources in the home, school, and broader community. This study emphasizes the links between siblings’ language ideologies, agentive decision making, and linguistic patterns, and the ways in which birth order influences the different dimensions of heritage language maintenance in the U.S..