This paper presents the results of a large-scale study to validate a questionnaire that measures pupils’ attitudes towards socioscientific issues (the PASSI questionnaire). We define socioscientific issues (SSI) as those topics that are about complex societal and technological developments that may induce ethical dilemmas. In this study, the term attitudes describes a combination of attitude components that relate to pupils’ engagement with SSI. Based on a literature review within social and educational psychology and sociology, on topics such as attitude development, scientific citizenship, social or civic engagement, and SSI teaching and learning, we developed a framework that describes several underlying components of pupils’ attitudes towards SSI. These components were translated into nine scales that comprise the PASSI. Results of a validation study among 1370 pupils (age 8–15), using exploratory factor analyses on subsample 1 and subsequently confirmatory factor analyses on subsample 2, indicated an eight-factor structure that showed good convergent and discriminant validity. Furthermore, the PASSI instrument showed adequate measurement invariance for boys and girls, pupils in primary and secondary education, and for pupils at different secondary educational tracks. The results are discussed in terms of directions for future research to further investigate the validity of the PASSI questionnaire. To conclude, the PASSI questionnaire validly measures eight attitudes towards SSI and could serve as a tool that raises awareness of pupils’ engagement with SSI. It can be used by researchers and teachers as a diagnostic instrument, to compare groups, and to study effects of SSI education.