Young people’s acquisition of knowledge about, and their development of and understanding of key concepts in, civics and citizenship is widely seen as an important function of most education systems. From a national perspective, civic knowledge would typically encompass aspects related to the country’s political system and its institutions, rights and responsibilities of citizens, mechanisms of engagement in society as well as general concepts (such as national identity, tolerance or shared values) (Schulz, Ainley, Fraillon, Kerr & Losito, 2010a & 2010b). Depending on the curriculum for civic and citizenship education in a country, it would be expected that these aspects could be defined in relation to the respective national context. From an international perspective, it is necessary to identify the common aspects of civics and citizenship which are shared across different countries. Examples of such common aspects include the recognition of shared principles, concepts and participatory mechanisms and motivations. It needs to be recognized that commonalities such as similar forms of government (for example, having a democratic system of government) would increase the likelihood of identifying shared cognitive aspects of civics and citizenship across different countries. Furthermore, it needs to be acknowledged that it is not possible to include in international assessment instruments questions about country-specific issues that address, for example, details about national institutions, constitutional arrangements or local civic issues. This paper describes how knowledge and understanding of civics and citizenship was assessed as part of the International Civic and Citizenship Education Study (ICCS 2009). ICCS 2009 was designed to investigate the ways in which young people in a range of countries are prepared and consequently ready and able to undertake their roles as citizens. Based on a comprehensive data collection in 38 countries from Europe, Latin America and the Asian-Pacific region the study reported on students’ knowledge and understanding, value beliefs and attitudes, activities and intended behaviours related to civics and citizenship (Schulz et al., 2010a & 2010b; Kerr, Sturman, Schulz & Burge, 2010; Schulz, Ainley, Lietz & Friedman, 2011). We will discuss previous research and the theoretical background for measuring civic knowledge and understanding, then describe the way it was measured in ICCS 2009 as well as methods employed to assess construct validity, and finally report selected outcomes of the assessment.