Until at least 6 mo of age, infants show good discrimination for familiar phonetic contrasts (i.e., those heard in the environmental language) and contrasts that are unfamiliar. Adult-like discrimination (significantly worse for nonnative than for native contrasts) appears only later, by 9-10 mo. This has been interpreted as indicating that infants have no knowledge of phonology until vocabulary development begins, after 6 mo of age. Recently, however, word recognition has been observed before age 6 mo, apparently decoupling the vocabulary and phonology acquisition processes. Here we show that phonological acquisition is also in progress before 6 mo of age. The evidence comes from retention of birth-language knowledge in international adoptees. In the largest ever such study, we recruited 29 adult Dutch speakers who had been adopted from Korea when young and had no conscious knowledge of Korean language at all. Half were adopted at age 3-5 mo (before nativespecific discrimination develops) and half at 17 mo or older (after word learning has begun). In a short intensive training program, we observe that adoptees (compared with 29 matched controls) more rapidly learn tripartite Korean consonant distinctions without counterparts in their later-acquired Dutch, suggesting that the adoptees retained phonological knowledge about the Korean distinction. The advantage is equivalent for the younger-adopted and the olderadopted groups, and both groups not only acquire the tripartite distinction for the trained consonants but also generalize it to untrained consonants. Although infants younger than 6 mo can still discriminate unfamiliar phonetic distinctions, this finding indicates that native-language phonological knowledge is nonetheless being acquired at that age.language acquisition | adoption | phonology | language memory T o talk to others, and to understand what others say, we need to know the phonological structure of the language we are using. Phonology embraces, for instance, the single-sound contrasts that distinguish one word from another, or the sequence constraints that apply to sounds; so if we are speaking English, we need to distinguish rye from lie, and if we hear [m] followed immediately by [b], we know that they belong to different syllables, as in somebody. Neither assumption holds for all languages. Phonological knowledge is highly language-specific.It is also abstract: not so much knowledge of the sounds and words in the language, but knowledge about those sounds and words, and the rules that govern them. Such knowledge is constantly called into play in adult talking and listening. When talkers must repeat others' utterances, they repeat the sounds that are said, but do so by using their own accent, not by imitating the accent in which the sounds are said (1). If talkers are exposed to novel phoneme sequence constraints in perception, they quickly apply them in production (2). In slips of the tongue, transposed elements accommodate to the new rather than to the originally intended phonetic context, su...