Cloud computing systems are becoming an important platform for science applications. Infrastructure as a Service (IaaS) clouds provide the capability to provision virtual machines (VMs) on demand with a specific configuration of hardware resources, but they do not provide functionality for managing those resources once provisioned. In order for such clouds to be used effectively for parallel and distributed scientific applications, tools need to be developed that can help users to deploy their applications in the cloud. This paper describes a system we have developed to provision, configure, and manage clusters of virtual machines. Categories and Subject Descriptors D.4.7 [Operating Systems]: Organization and Design–distributed systems. General Terms: Management, Design.