Citizenship has recently been introduced into the educational curriculum. Instruments to determine the effects of citizenship education are scarce. In this article, the concept of citizenship competences is explored in order to develop a measurement instrument. Four social tasks were derived from the literature as representative of young people's citizenship practices: acting democratically, acting in a socially responsible manner, dealing with conflicts, and dealing with differences. What adequate fulfilment of each social task presupposes in terms of knowledge, attitudes, skills, and reflection is defined per task and operationalised into items for a questionnaire. The sample (N = 16,000) concerns a representative sample of students in grade 6 and grade 9. Confirmatory factor analyses were conducted to determine the extent to which the structure in the data corresponded to the structure expected on theoretical grounds. The study reveals a reliable and valid instrument for the measurement of young people's citizenship competences. Future research should provide insight into how these competences relate to citizenship behaviour and whether measures of citizenship competences and behaviour will help schools to evaluate the effectiveness of their efforts.