The Skills Imperative 2035 is a five-year strategic research programme, funded by the Nuffield Foundation, which is investigating future skills needs, skills supply and skill development, with a particular focus on the 'Essential Employment Skills' (EES) that are projected to be most vital across the labour market in 2035. The focus in this stage of the programme is on the factors which explain cross-country variation across a broader set of related cognitive and socio-emotional skills, in line with the hypothesis that young people's cognitive and socio-emotional skills are antecedents for their EES in early adulthood. These EES then, in turn, are likely to have a significant bearing on young people's ability to enter, or progress into, growing, predominantly professional, occupations. This paper investigates cross-country differences across a range of measures in young people's cognitive, socio-emotional and self-management skills using data from International Large Scale Assessments (ILSAs) and identifies education system factors associated with higher performance. Based on these comparisons, the authors identify countries that are relatively high-performing on at least one of the skills measures, identify common features associated with higher skills outcomes in those countries, and examine how these features are combined and implemented in seven 'high performing' countries, compiling case studies on each and summarising what can be learned from these cases. The summary report which accompanies this report explores the research implications for how future skills needs might be met in England, particularly the growing demand for EES.