Spreadsheet languages, which include commercial spreadsheets and various research systems, have proven to be flexible tools in many domain specific settings. Research shows, however, that spreadsheets often contain faults. We would like to provide at least some of the benefits of formal testing and debugging methodologies to spreadsheet developers. This paper presents an integrated testing and debugging methodology for spreadsheets. To accommodate the modeless and incremental development, testing and debugging activities that occur during spreadsheet creation, our methodology is tightly integrated into the spreadsheet environment. To accommodate the users of spreadsheet languages, we provide an interface to our methodology that does not require an understanding of testing and debugging theory, and that takes advantage of the immediate visual feedback that is characteristic of the spreadsheet paradigm.