The Improved Limb Atmospheric Spectrometer--II (ILAS-II) was a solar-occultation satellite sensor designed to measure minor constituents associated with polar ozone depletion. ILAS-II was placed on board the Advanced Earth Observing Satellite--II (ADEOS-II, "Midori-II"), which was successfully launched on 14 December 2002 from the Tanegashima Space Center of the Japan Aerospace Exploration Agency (JAXA). After an initial check of the instruments, ILAS-II made routine measurements for about 7 months, from 2 April 2003 to 24 October 2003, a period that included the formation and collapse of an Antarctic ozone hole in 2003, one of the largest in history. This paper introduces a special section containing papers on ILAS-II instrumental and on-orbit characteristics, several validation results of ILAS-II data processed with the version 1.4 data processing algorithm, and scientific analyses of polar stratospheric chemistry and dynamics using ILAS-II data.