We develop a powerdomain construction, $\mathcal{P}[ \cdot ]$, which is analogous to the powerset construction and also fits in with the usual sum, product and exponentiation constructions on domains. The desire for such a construction arises when considering programming languages with nondeterministic features or parallel features treated in a nondeterministic way. We hope to achieve a natural, fully abstract semantics in which such equivalences as $(p\textit{ par } p) = (q\textit{ par }p)$ hold. The domain ($D \to $ Truthvalues) is not the right one, and instead we take the (finitely) generable subsets of D. When D is discrete they are ordered in an elementwise fashion. In the general case they are given the coarsest ordering consistent, in an appropriate sense, with the ordering given in the discrete case. We then find a restricted class of algebraic inductive partial orders which is closed under $\mathcal{P}[ \cdot ]$ as well as the sum, product and exponentiation constructions. This class permits the...