In this chapter, we discuss the development, architecture, and functionality of the National Partnership for Advanced Computational Infrastructure NPACI Grid Portals project. The emphasis of this paper is on the NPACI Grid Portal Toolkit (GridPort); we also discuss several Grid portals built using GridPort including the NPACI HotPage. We discuss the lessons learned in developing this toolkit and the portals built from it, and finally we present our current and planned development activities for enhancing GridPort and thereby the capabilities, flexibility, and ease-of-development of portals built using GridPort | 28 Building Grid computing portals the NPACI Grid portal toolkit Mary P. Thomas and John R. Boisseau The University of Texas at Austin Austin Texas United States INTRODUCTION In this chapter we discuss the development architecture and functionality of the National Partnership for Advanced Computational Infrastructure NPACI Grid Portals project. The emphasis of this paper is on the NPACI Grid Portal Toolkit GridPort we also discuss several Grid portals built using GridPort including the NPACI HotPage. We discuss the lessons learned in developing this toolkit and the portals built from it and finally we present our current and planned development activities for enhancing GridPort and thereby the capabilities flexibility and ease-of-development of portals built using GridPort. What are Grid computing portals Web-based Grid computing portals or Grid portals 1 have been established as effective tools for providing users of computational Grids with simple intuitive interfaces for accessing Grid information and for using Grid resources 2 . Grid portals are now being Grid Computing - Making the Global Infrastructure a Reality. Edited by F. Berman A. Hey and G. Fox 2003 John Wiley Sons Ltd ISBN 0-470-85319-0 676 MARY P. THOMAS AND JOHN R. BOISSEAU developed deployed and used on large Grids including the National Science Foundation NSF Partnership for Advanced Computational Infrastructure PACI TeraGrid the NASA Information Power Grid and the National Institute of Health NIH Biomedical Informatics Research Network. Grid middleware such as the Globus Toolkit provides powerful capabilities for integrating a wide variety of computing and storage resources instruments and sensors but Grid middleware packages generally have complex user interfaces UIs and Application Programming Interfaces APIs . Grid portals make these distributed heterogeneous compute and data Grid environments more accessible to users and scientists by utilizing common Web and UI conventions. Grid .