An archive of monthly temperatures, dew points, geopotentials, and winds at standard tropospheric and stratospheric levels from about 800 rawinsonde stations has been developed from routinely transmitted monthly data, and supplemented with published or national archive data. Many stations' data commence in the 1950s and the archive is continually updated. The raw data, however, contain both random and systematic errors. Quality control of random errors includes hydrostatic, wind-shear, and climatological checks, and comparisons with neighbouring stations and operational model analyses. Systematic errors in the wind speeds have resulted from the inadequately documented use of knots by some nations and metres per second by others in monthly messages. These errors are being amended by using geopotential height gradients, by comparing wind speeds reported from opposite sides of national borders, by averaging independently coded and transmitted daily data, and by the acquisition of original data from national archives. Other systematic errors result from changes of rawinsonde instrumentation, evolving operationally applied radiation and lag corrections, and changes of ascent times. Accordingly, the archive includes station histories where available, but these are far from complete. If the data are to be used in trustworthy analyses of interannual and longer term climatic variations, adjustments will need to be applied, using fully documented station histories and a knowledge of the effects of instrumental and other changes. Techniques for estimation of systematic adjustments include comparisons between neighbouring stations, comparisons with operational model analyses, the use of extended international radiosonde comparisons, and models of the thermodynamics of radiosonde instruments.