Synopsis The set of scientists included in our sample is not necessarily representative of any sociological category. We searched out people who had completed or nearly completed their careers. We believed that such lives would contain a richer stock of information, and more personal insights into the characteristics of a career in research, than would the lives of those earlier in their career. However, we realized that so much has changed during the twentieth century that we needed to include younger scientists to illustrate more accurately the conditions that prevail today, as well as to show what a scientific career in the upcoming century might entail.