Abstract: This paper describes the management of heterogeneity in Stardust, an environment for parallel programming above networks of heterogeneous machines, which can include distributed memory multicomputers and networks of workstations. Applications using Stardust can communicate both through message passing and distributed shared memory. Stardust is currently implemented on an heterogeneous system including an Intel Paragon running Mach/OSF1 and an ATM network of Pentiums running Chorus/classiX. The paper details the design and implementation of Stardust, as well as its performance.