It is known that most simply connected 4-manifolds admit infinitely many
"exotic" smooth structures, but the existence of such structures is
still unknown for S^4 and CP^2.  We report on the current state of art
of exotic structures on rational surfaces, and review how such
structures can be constructed. The main ingredients are the rational
blow-down process and the computation of appropriate Seiberg-Witten
invariants. We also discuss the classification of plumbing trees which
can be symplectically blown down.