In the international computer and information literacy study (ICILS), student outcomes associated with computer and information literacy (CIL) and computational thinking (CT) are assessed using separate instruments. Contextual data that can be used to explain variations in CIL and CT are collected through questionnaires completed by students, teachers, ICT-coordinators, school principals, and through a national contexts survey. Providing an in-depth look at the design and evolution of the ICILS test instruments, this chapter highlights the adaptation of the test design to reflect the evolving landscape of real-world digital technologies and authentic assessment scenarios. It elaborates on the diversity of assessment tasks, including information-based response tasks that evaluate students’ ability to retrieve and process information, skills tasks that assess practical ICT skills, and authoring tasks that gauge students’ ability to create and edit digital content. Furthermore, the chapter delves into the methodology of mapping test items to the CIL and CT constructs from Chaps. 3 and 4, demonstrating how the skills and knowledge articulated by the construct definitions are represented by the test instruments. The chapter concludes with summary information of the contents of the questionnaire instruments.