We describe the execution and data reduction of the European SouthernObservatory Large Programme "Quasars and their absorption lines: alegacy survey of the high-redshift Universe with VLT/X-shooter"(hereafter "XQ-100"). XQ-100 has produced and made publicly available ahomogeneous and high-quality sample of echelle spectra of 100 quasars(QSOs) at redshifts z ≃ 3.5-4.5 observed with full spectralcoverage from 315 to 2500 nm at a resolving power ranging from R ~ 4000to 7000, depending on wavelength. The median signal-to-noise ratios are33, 25 and 43, as measured at rest-frame wavelengths 1700, 3000 and 3600Å, respectively. This paper provides future users of XQ-100 datawith the basic statistics of the survey, along with details of targetselection, data acquisition and data reduction. The paper accompaniesthe public release of all data products, including 100 reduced spectra.XQ-100 is the largest spectroscopic survey to date of high-redshift QSOswith simultaneous rest-frame UV/optical coverage, and as such enables awide range of extragalactic research, from cosmology and galaxyevolution to AGN astrophysics.Based on observations made with ESO Telescopes at the La Silla ParanalObservatory under programme ID 189.A-0424.The XQ-100 raw data and theXQ-100 Science Data Products can be found at http://archive.eso.org/eso/eso_archive_main.htmland http://archive.eso.org/wdb/wdb/adp/phase3_main/form,respectively.