This article starts with a brief description of the phenomenon of song learning in birds, and then outlines various consequences that it has for the individuals that show it and the groups to which they belong. Among these are the following features, each of which has been described in at least some species: the sharing of song between kin and between neighbours; changes in song with time; changes with distance, including the phenomenon of dialects. The final section is a discussion of which of these consequences may have functional significance and so be likely to be an advantage of song learning. It is suggested that cultural evolution, geographical variation and dialect boundaries, being features of populations rather than individuals, are epiphenomena without functional significance in themselves. However, song learning may confer advantages stemming from the copying process itself, in interactions with neighbours and in matching song to habitat. The evidence that learnt dialects have a role in assortative mating is less convincing. It is likely both that song learning has different functions in different species, and that it has more than a single function in many of them.