Prior to the International Computer and Information Literacy Study (ICILS), research into learning outcomes related to information and computer technologies (ICT), and factors associated with student achievement in this area had generally been based on a few national studies. ICILS 2018 used multilevel models to assess the extent to which factors at the student and school level were associated with variations in computer and information literacy (CIL) and computational thinking (CT). It investigated access to, use of, and familiarity with ICT, school context factors, as well as variables reflecting the personal and social background of students. There were differences in the variance in both CIL and CT, as well as the proportion of variance between schools, across participating countries. Multilevel models explained much of the variance in CIL and CT at the school level but less variance within schools was explained. Personal and social background factors were shown to be associated with CIL and CT. Female students tended to have higher CIL scores than male students but lower CT scores than male students. The use of the test language at home was a positive predictor of CIL and CT in some countries. Both expected university education and socioeconomic background were consistent positive predictors of both CIL and CT across countries. There were mostly inconsistent effects across countries on CIL and CT by school-level factors related to ICT.