In Denmark about one fifth of all researchers at the universities are female. 92 per cent of all full professors are men. This uneven distribution of men and women in the research community has been constant for many years, and does not seem to change dramatically in the near future. The main point in the paper is to demonstrate that this is not a simple problem but at complex of problems, which need to be analysed, understood and changed in that respect. A number of hypotheses are presented in an analytical framework in which I distinguish between different levels. Some of the hypotheses are discussed and preliminary answers given.