Higher Order Invariants in Supergravity
  On a historical note, we first describe the early superspace construction of counterterms in supergravity and then move on to a brief discussion of selected areas in string theory where higher order supergravity invariants enter the effective theories. Motivated by this description we argue that it is important to understand $p$-brane actions with $\k$-invariant higher order terms, thus re-opening the question of $\k$-invariant ``rigidity'' terms. Finally we describe a recent construction of such an action using the superembedding formalism. 
Ulf Lindstrom