Pegasus is an open-source workflow management system. It provides the necessary abstractions for scientists to create scientific workflows and allows for transparent execution of these workflows on a range of computing platforms including high performance computing clusters, clouds, and national cyberinfrastructure. In Pegasus, workflows are described abstractly as directed acyclic graphs (DAGs) using a provided API for Jupyter Notebooks, Python, R, or Java. During execution, Pegasus translates the constructed abstract workflow into an executable workflow which is executed and managed by HTCondor.