XOP (X-ray OPtics utilities) is a graphical user interface (GUI) to run computer programs that calculate basic information needed by synchrotron radiation beamline scientists and engineers. It can also be used as a front end for specific codes or packages for data analysis and data reduction (XAFS, surface crystallography, etc.). XOP contains a customized database for optical and atomic constants. It has a flexible design and new applications may be added. The capabilities of XOP, including those related to simulations of crystal diffraction profiles and multilayer reflectivities, are summarized. We discuss the most recent developments to be included in XOP version 2.0. A few other examples of typical calculations are: insertion device (undulator and wiggler) spectra and angular distributions, mirror and multilayer reflectivities, and crystal diffraction profiles. The computer programs are executed and the results are analyzed within the GUI, which makes them fast and easy to use. The XOP interface is written in the Interactive Data Language (IDL) from Research Systems Inc., and it runs on the Unix (HP, Sun, Linux, DEC-Alpha, and Silicon Graphics), and on the Windows 95/NT operating systems. It has been built with an IDL license embedded and is available under some limited conditions free of charge from the authors.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.