The Swift Gamma-Ray Burst Explorer (Gehrels et al., 2004) was selected as NASA's next MIDEX mission in October 1999 and launched on 20 November 2004. It carries three instruments: a Burst Alert Telescope (BAT), an Ultraviolet/Optical Telescope (UVOT), and an X-ray Telescope (XRT). The XRT is a sensitive, flexible, autonomous X-ray imaging spectrometer designed to measure fluxes, spectra, and lightcurves of Gamma-Ray Bursts (GRBs) and afterglows over a wide dynamic range of more than 7 orders of magnitude in flux. The XRT uses a grazing incidence Wolter I telescope to focus X-rays onto a thermoelectrically cooled CCD. The XRT is designed to provide accurate positions within 5 seconds of target acquisition for typical bursts, allowing ground-based optical telescopes to begin immediate spectroscopic observations of the afterglow. The XRT has an effective area of > 120 cm² at 1.5 keV, a field of view of 23.6 x 23.6 arcminutes, and an angular resolution of 18 arcseconds (HPD). The detection sensitivity is 2x10⁻¹⁴ erg cm⁻² s⁻¹ in 10⁶ seconds. The XRT operates in an auto-exposure mode, adjusting the CCD readout mode automatically to optimize the science return for each frame as the source intensity fades. The XRT will measure spectra and lightcurves of the GRB afterglow beginning about a minute after the burst and will follow each burst for days or weeks. The XRT is designed to provide automated source detection and position reporting within 5 seconds of target acquisition. It can also measure the redshifts of GRBs with Fe line emission or other spectral features. The XRT is a sensitive, flexible, autonomous X-ray imaging spectrometer designed to measure fluxes, spectra, and lightcurves of GRBs and afterglows over a wide dynamic range of more than 7 orders of magnitude in flux. The XRT is designed to provide accurate positions within 5 seconds of target acquisition for typical bursts, allowing ground-based optical telescopes to begin immediate spectroscopic observations of the afterglow. The XRT uses a grazing incidence Wolter I telescope to focus X-rays onto a thermoelectrically cooled CCD. The XRT is designed to provide accurate positions within 5 seconds of target acquisition for typical bursts, allowing ground-based optical telescopes to begin immediate spectroscopic observations of the afterglow. The XRT is a sensitive, flexible, autonomous X-ray imaging spectrometer designed to measure fluxes, spectra, and lightcurves of GRBs and afterglows over a wide dynamic range of more than 7 orders of magnitude in flux. The XRT is designed to provideThe Swift Gamma-Ray Burst Explorer (Gehrels et al., 2004) was selected as NASA's next MIDEX mission in October 1999 and launched on 20 November 2004. It carries three instruments: a Burst Alert Telescope (BAT), an Ultraviolet/Optical Telescope (UVOT), and an X-ray Telescope (XRT). The XRT is a sensitive, flexible, autonomous X-ray imaging spectrometer designed to measure fluxes, spectra, and lightcurves of Gamma-Ray Bursts (GRBs) and afterglows over a wide dynamic range of more than 7 orders of magnitude in flux. The XRT uses a grazing incidence Wolter I telescope to focus X-rays onto a thermoelectrically cooled CCD. The XRT is designed to provide accurate positions within 5 seconds of target acquisition for typical bursts, allowing ground-based optical telescopes to begin immediate spectroscopic observations of the afterglow. The XRT has an effective area of > 120 cm² at 1.5 keV, a field of view of 23.6 x 23.6 arcminutes, and an angular resolution of 18 arcseconds (HPD). The detection sensitivity is 2x10⁻¹⁴ erg cm⁻² s⁻¹ in 10⁶ seconds. The XRT operates in an auto-exposure mode, adjusting the CCD readout mode automatically to optimize the science return for each frame as the source intensity fades. The XRT will measure spectra and lightcurves of the GRB afterglow beginning about a minute after the burst and will follow each burst for days or weeks. The XRT is designed to provide automated source detection and position reporting within 5 seconds of target acquisition. It can also measure the redshifts of GRBs with Fe line emission or other spectral features. The XRT is a sensitive, flexible, autonomous X-ray imaging spectrometer designed to measure fluxes, spectra, and lightcurves of GRBs and afterglows over a wide dynamic range of more than 7 orders of magnitude in flux. The XRT is designed to provide accurate positions within 5 seconds of target acquisition for typical bursts, allowing ground-based optical telescopes to begin immediate spectroscopic observations of the afterglow. The XRT uses a grazing incidence Wolter I telescope to focus X-rays onto a thermoelectrically cooled CCD. The XRT is designed to provide accurate positions within 5 seconds of target acquisition for typical bursts, allowing ground-based optical telescopes to begin immediate spectroscopic observations of the afterglow. The XRT is a sensitive, flexible, autonomous X-ray imaging spectrometer designed to measure fluxes, spectra, and lightcurves of GRBs and afterglows over a wide dynamic range of more than 7 orders of magnitude in flux. The XRT is designed to provide