Abstract : Cloud technologies provide many benefits for scientific and engineering applications, such as customised execution environments, near-instantaneous provisioning, elasticity, and the ability to run user-level services. However, a rapid, wholesale shift to using public, commercial cloud services is unlikely because of capital investments in existing resources and data management issues. To take full advantage of cloud technologies in the short term, institutes and companies must be able to deploy their own cloud infrastructures. The StratusLab project provides a complete, open-source cloud distribution that permits them to do this. The StratusLab services include the computing, storage, and networking services required for an Infrastructure as a Service (IaaS) cloud. It also includes high-level services like the Marketplace that facilitates the sharing of machine images and Claudia that allows the deployment and management of complete software systems.