Investigators of bilingual language acquisition have underscored the fact that the child growing up with two languages provides us with an ideal natural experiment. First, the bilingual child offers welcome opportunities for disentangling general cognitive and specific linguistic development. Second, the investigator can look at different language policies adopted by individual families and caregivers, compare features of the respective input, and relate these features to the child's emerging language systems and communicative behavior. Lanza's book addresses this second set of issues and provides us with valuable insights concerning what she calls “language socialization” and children's early sensitivity toward the acceptability of their language choice.