  We are on the way to obtaining multi-dimensional "pictures" of the proton.
The field is bursting with activities, both from the theoretical and
experimental side. A brief selection of important achievements of the last
years and open challenges for the future is presented. They are already well
documented in the various reviews of this Special Issue, but they are gathered
here in a more condensed way for convenience, together with some additional
remarks. The choice of the items included in this short overview is far from
being complete and represents the view of the author.
