This chapter outlines the design and implementation of the International Computer and Information Literacy Study (ICILS) 2023 computer and information literacy (CIL) test instrument, emphasizing its relevance to assessing students’ digital competencies in realistic and educationally meaningful contexts. The chapter begins by introducing the foundational principles of the CIL framework, which defines CIL as the ability to use computers for investigating, creating, and communicating. The framework organizes the CIL construct into four strands: understanding computer use, gathering information, producing information, and digital communication. The chapter details the development and refinement of the CIL test modules, which incorporate tasks that simulate real-world scenarios to assess technical, receptive, productive, and evaluative skills. These modules also test students’ understanding of ethical and responsible information and communication technology (ICT) use. The ICILS CIL achievement scale, established in 2013, is presented alongside its iterative updates across study cycles to ensure alignment with evolving digital tools and educational practices. Students’ achievements are classified into four described proficiency levels, ranging from basic functional use through to precise and discerning use. The chapter concludes with examples from released test materials, demonstrating practical applications of the CIL framework and providing educators with insights to support targeted CIL learning outcomes.