Plethysms of symmetric functions correspond to compositions of representations of GL(n,C). Explicit expansions of plethysms of one Schur function into another in terms of the Schur basis are known only in a few "small" cases, and most of them are decades old. I will present a compact way to package those in certain rational generating functions, as well as some evidence that similar, although much less compact, descriptions exist in cases that have not been worked out explicitly.