The primary purpose of International Computer and Information Literacy Study (ICILS) 2018 is to assess systematically the capacities of students to use ICT productively for a range of different purposes, in ways that go beyond a basic use of ICT. ICILS 2018 includes authentic computer-based assessments that are administered to students in their eighth year of schooling. A secondary purpose of ICILS 2018 is to investigate the use of computers and other digital devices by students and teachers, as well as their attitudes toward the use of computer technologies. Some of these aspects of computer use are directly related to student outcomes, while others may not be directly associated with them but may inform understanding of the broader context in which computer technologies are used both within and outside school. Further contextual information is provided by schools and education systems about the policies, resources, and pedagogies regarding computer technologies. The ICILS assessment framework articulates the basic structure of the study. It provides a description of the field and the constructs to be measured. It outlines the design and content of the measurement instruments, sets down the rationale for those designs, and describes how measures generated by those instruments relate to the constructs. In addition, it hypothesizes relations between constructs so as to provide the foundation for some of the analyses that follow. Above all, the framework links ICILS to other work in the field so that the contents of this assessment framework combine theory and practice in an explication of "both the 'what' and the 'how'" (Jago 2009, p. 1) of ICILS. The ICILS 2018 assessment framework is based on the ICILS 2013 framework, but has been adapted and amended to address new challenges for ICILS 2018, an innovative trend study posed by evolving educational requirements. [This work was published by SpringerOpen. For the ICILS 2013 framework, "International Computer and Information Literacy Study: Assessment Framework," see ED545260.]