Flight performance is an important aspect of avian biology, potentially affecting the energetics, life history, ecology, dispersal, and evolution of birds. Yet measuring flight performance directly can be challenging and time intensive. Here we discuss morphological proxies of flight performance that can be measured from museum specimens. These include wing shape, wing size, and flight muscle size. We provide details on how to obtain indices of these characters from traditional round study skin specimens as well as from new specimen types, such as spread wings and skeletons. We also offer suggestions for specimen preparators on how to maximize the usefulness of specimens for studies of flight performance. Finally, we discuss recent applications of the use of museum specimens in studies of flight performance and dispersal, including how dispersal ability relates to diversification and how flight constrains genome size.