Calibration of the point spread function for the RGS on XMM

We present the results of the point spread function calibration performed on the Reflection Grating Spectrometer of XMM. This calibration was done at the long-beam X-ray testing facility at Panter, Munich, Germany, and the analysis recently completed. Contributions to the spectrometer's PSF arise mainly from the focusing mirror PSF, grating surface micro-roughness and nonflatness, and deviations from perfect hardware positioning within specifications. The predicted model, which was mainly based on these effects, was consistent with extensive experimental results to within a few percent over a wide range of parameter space, slightly greater than will be used in flight. We will also present the in-flight calibration program for the post-launch refinement of the RGS PSF.