This study examines pragmatic differentiation in early trilingual development through a longitudinal analysis of language choice in a developing Tagalog-Spanish-English trilingual child. The child's patterns of language choice with different language users are analyzed at age 1 ; 10 and 2 ; 4 to examine: (1) whether evidence for pragmatic differentiation can be found even before age two and in simultaneous interactions with distinct language users; (2) whether lexical gaps determine the child's choice of one language over another; and (3) whether her patterns of language choice are affected by the interlocutors language use and their responses to mixing. The results indicate that the child was capable of selecting the appropriate language according to the interlocutors' language from the earliest sessions. However, switches to inappropriate languages were common due to vocabulary gaps, the interlocutors' acceptance of mixing and the possibilities determined by the existence of multiple lexical resources and multiple language users.