A project of the National Science Foundation, the TeraGrid is "a multi-year effort to build and deploy the world's largest, fastest, distributed infrastructure for open scientific research." This paper, published in September 2002, describes the activities and ongoing projects that will ultimately lead to the project's completion. TeraGrid, as the name implies, is based on principles of grid computing. It will eventually consist of a massive network of computers spread out over several sites that can work simultaneously and independently on scientific applications. Many specifications and design objectives are outlined in the paper, offering some insight into the ambitious project.