  The First Data Release (DR1) of the UKIRT Infrared Deep Sky Survey (UKIDSS)
took place on 2006 July 21. UKIDSS is a set of five large near-infrared
surveys, covering a complementary range of areas, depths, and Galactic
latitudes. DR1 is the first large release of survey-quality data from UKIDSS
and includes 320 sq degs of multicolour data to (Vega) K=18, complete
(depending on the survey) in three to five bands from the set ZYJHK, together
with 4 sq degs of deep JK data to an average depth K=21. In addition the
release includes a similar quantity of data with incomplete filter coverage. In
JHK, in regions of low extinction, the photometric uniformity of the
calibration is better than 0.02 mag. in each band. The accuracy of the
calibration in ZY remains to be quantified, and the same is true of JHK in
regions of high extinction. The median image FWHM across the dataset is 0.82
arcsec. We describe changes since the Early Data Release in the implementation,
pipeline and calibration, quality control, and archive procedures. We provide
maps of the areas surveyed, and summarise the contents of each of the five
surveys in terms of filters, areas, and depths. DR1 marks completion of 7 per
cent of the UKIDSS 7-year goals.
