This paper is based on a comparative study on Ultraviolet radiation (UV) measurements and UV reconstructions models for eight sites in Europe. Reconstruction models include neural network techniques and radiative transfer modeling combined with empirical relationships. The models have been validated against quality controlled ground-based measurements - 8 to 20 years - on time scales ranging from daily to yearly UV sums. The standard deviations in the ratios of modeled to measured daily sums vary between 10 to 15%. The yearly sums agree within a 5% range. Depending on the availability of ancillary measurements, reconstructions have been carried out to the early sixties. A method has been set up to educe one best estimate of the historical UV levels that takes into account the long-term stability and underlying agreement of the models, and the agreement with actual UV measurements. Using this best estimate, the yearly sums of erythemally weighted UV irradiance showed a range of 300 kJ/m2 at 67 degrees north to 750 kJ/m2 at 40 degrees north. The year-to-year variability was lowest at 40 degrees north with a relative variation of 4.3%; for central and northern European latitudes this year-toyear variation was 5.2 to 6.5%. With regard to the period 1980 to 2006, first order trend lines range from 0.3 ± 0.1 to 0.6 ± 0.2 % per year, approximately two thirds of which can be attributed to the diminishing of cloudiness and one third to ozone decline.