It has been shown by Trudinger and Moser that for normalized functions u of the Sobolev space W 1,N ( ), where is a bounded domain in R N , one has exp(α N |u| N /(N −1) )dx ≤ C N , where α N is an explicit constant depending only on N , and C N is a constant depending only on N and . Carleson and Chang proved that there exists a corresponding extremal function in the case that is the unit ball in R N . In this paper we give a new proof, a generalization, and a new interpretation of this result. In particular, we give an explicit sequence that is maximizing for the above integral among all normalized "concentrating sequences." As an application, the existence of a nontrivial solution for a related elliptic equation with "Trudinger-Moser" growth is proved.