Exactly a decade ago an international conference on solar physics took place in Utrecht on the occasion of the late Prof. Minnaert’s 70th birthday. Since then, much has happened. Many new instrumental devices were developed or refined. Completely new observational techniques were applied in the XUV and radio wavelengths and in particle detection.

This all resulted in an explosion of new data. Moreover new problems appeared of course. It also resulted in an explosion of papers on solar physics. Actually many more contributions appear than reasonably can be absorbed by the periodical Solar Physics, of which the first volume appeared in 1967. At that time the editors were not at all sure that they would receive enough papers to maintain such a journal. But were there major problems solved recently?

At first I would be inclined to think that, notwithstanding the enormous efforts spent in solar physics, little has been achieved and no spectacular breakthroughs have been found. This impression, probably shared by many more colleagues, becomes stronger if one tries to find a line of progress in ‘classical’ problems of solar physics. We still do not have a satisfactory theory of the Sun’s differential rotation and the Sun’s outer convection zone. One may argue that this is due to our bad knowledge of the interior structure which is not accessible to direct observation. Solar activity and the formation of sunspots is now believed to be a direct consequence of differential rotation and cyclonic convective motions and therefore suffers from the same uncertainties.