The Pegasus Workflow Management System encompasses a set of technologies which help workflow-based applications execute in a number of different environments, including desktops, campus clusters, grids, and clouds. It bridges the scientific domain and the execution environment by automatically mapping high-level workflow descriptions onto distributed resources. It automatically locates the necessary input data and computational resources necessary for workflow execution. It enables scientists to construct workflows in abstract terms without worrying about the details of the underlying execution environment or the particulars of the low-level specifications required by the middleware (Condor, Globus, or Amazon EC2). It bridges the current cyberinfrastructure by effectively coordinating multiple distributed resources.