This chapter addresses the questions of how to explore the knowledge and skills teachers need for effectively integrating technology in their teaching in an international study. It begins by underlining the importance of including technology-related knowledge in an assessment of teachers’ pedagogical knowledge for teaching in the 21st century. Then, it outlines the type of knowledge and skills teachers need for effectively integrating technology in their teaching and how these can be measured across countries. Drawing on previous research, different measurement approaches will be discussed. Despite a focus on teacher knowledge, the chapter includes suggestions for exploring teacher knowledge in the broader context of teachers' overall conditions, attitudes, and application of technology in teaching practice.