Although the majority of oscine species acquire a song repertoire by imitating songs they have been exposed to, some species also improvise and invent songs. To test the hypothesis that American Robins (Turdus migratorius) both imitate and invent the elements of their whistle songs, I analyzed the song repertoires of wild robins at three locations in western Massachusetts and the song development of five tutor-trained nestling robins. Robins appear to invent or improvise most of the elements in their repertoires (75–82%), but as fledglings and juveniles they acquire the remaining elements by imitating the songs of neighboring birds.