This study analyzes the beliefs about science-technology-society, and other Nature of Science (NOS) themes, of a large sample (613) of Spanish pre- and in-service secondary education teachers through their responses to 30 items of the Questionnaire of Opinions on Science, Technology and Society. The data were processed by means of a multiple response model to generate the belief indices used as the bases for subsequent quantitative and qualitative analyses. Other studies have reported a negative profile of teachers' understanding in this area, but the diagnosis emerging from the present work is more complex. There was a mix of appropriate beliefs coexisting with others that are inappropriate on the topics analyzed. The overall assessment, however, is negative since clearly teachers need to have a better understanding of these questions. There were scant differences between the pre- and in-service teachers, and hence no decisive evidence that the practice of teaching contributes to improving the in-service teachers' understanding. These results suggest there is an urgent need to bring the initial and continuing education of science teachers up to date to improve their understanding of these topics of science curricula, and thus improve the teaching of science.