  Iterated function systems (IFSs) are one of the most important tools for
building examples of fractal sets exhibiting some kind of `approximate
self-similarity'. Examples include self-similar sets, self-affine sets etc. A
beautiful variant on the standard IFS model was introduced by Barnsley and
Demko in 1985 where one builds an \emph{inhomogeneous} attractor by taking the
closure of the orbit of a fixed compact condensation set under a given standard
IFS. In this expository article I will discuss the dimension theory of
inhomogeneous attractors, giving several examples and some open questions. I
will focus on the upper box dimension with emphasis on how to derive good
estimates, and when these estimates fail to be sharp.
