Hugo Hadwiger proved in 1957 that any continuous rigid-motion-invariant valuation on the set of compact convex sets in Rn can be written as a linear combination of the intrinsic volumes. Daniel Klain, through some clever “cut and paste” arguments and a trick involving zonoids, was able to shorten the proof. This talk will discuss what valuations and intrinsic volumes are and then outline Klain’s proof of the theorem.