This article focuses on scientific knowledge as one aspect of the scientific competencies that citizens should ideally possess. The analysis is based on a Delphi study we conducted with Spanish experts from different science-related fields. The results showed that although the experts proposed several examples of scientific knowledge, the degree of consensus reached fell short of the minimum criterion we established. This article seeks to identify the reasons for this lack of consensus by examining the ways in which scientific knowledge was regarded in this Delphi study, the results of which are also compared with other relevant studies on science education for citizens. The analysis reveals that the different professional groups consulted did not, at the start of the Delphi process, place the same degree of emphasis on scientific knowledge. They also differed both in the importance ratings they awarded to the areas of scientific knowledge that had been proposed by the panel as a whole, and in the degree of variance shown by the ratings of each group. Comparison of the present results with the content of previous studies support the importance of selecting a small, common core of scientific knowledge that has both intrinsic and educational value.