The project is aimed at service provisioning, networking and research of cloud and virtualization technologies to simplify and optimize the use and operation of existing distributed computing infrastructures (e.g. EGEE/EGI). The project will incorporate cloud and virtualization innovation into existing Grid infrastructures by integrating cloud technologies and services within Grid sites; and by enriching existing computing infrastructures with "Infrastructure as a Service" (IaaS) cloud-like delivery paradigms.StratusLab will integrate, distribute and maintain a sustainable open-source cloud distribution to bring cloud to existing and new grid sites. The StratusLab toolkit will be composed of existing cutting-edge open source software, and the innovative service and cloud management technologies developed in the project. It will also include the required additions to turn the software elements into a production grade distribution to support production quality and operational systems, as will be demonstrated with the operation of production level grid sites in the project.StratusLab will bring to the e-Infrastructure ecosystem several benefits, in terms of simplification, added flexibility, increased maintainability, quality, energy efficiency and resilience of the sites. The new distribution will complement existing middleware services, being fully transparent to upper layers in the infrastructure. Existing Grid middleware would continue to provide the glue to federate the distributed resources and the services for high-level job and data management. StratusLab will help to improve usability of distributed computing infrastructures, attracting the science user communities and industrial users that have embraced the cloud computing provisioning model; to keep European research infrastructures at the technology forefront; and to strengthen the technological know-how in virtualization and cloud computing of the European industry.