I would like to dedicate this paper to the memory of my husband, Henryk Iwaniszewski, an astronomer working in radio astronomy and electronics, who until his untimely death seven years ago had been very active as president of our local branch of the Polish Amateur Astronomers Association. He was especially keen about introducing astronomy to the general public.

I want to speak here mainly, but not exclusively, about the IAU Colloquium No. 98, “Contribution of Amateur Astronomers to Astronomy,” which was held in 1988 in Paris. First of all, some definitions. Thomas Williams of the American Association of Variable Star Observers (AAVSO), from Houston, Texas, introduced at the conference several criteria for identification — first of astronomers, and then of professionals and amateurs. According to Williams: