The Pegasus project encompasses a set of technologies the help workflow-based applications execute in a number of different environments including desktops, campus clusters, grids, and now clouds. Scientific workflows allow users to easily express multi-step computations, for example retrieve data from a database, reformat the data, and run an analysis. Once an application is formalized as a workflow the Pegasus Workflow Management Service can map it onto available compute resources and execute the steps in appropriate order.