This paper presents a framework for studying international differences in the distribution of household income. Integrating micro-econometric and micro-simulation approaches in a decomposition analysis, it quantifies the role of tax-benefit systems, employment and occupational structures, labour and financial market returns, and demographic composition in accounting for differences in income inequality across countries. Building upon EUROMOD (the European tax-benefit calculator) and its harmonised datasets, the model is portable and can be implemented for cross-country comparisons between any participating country. An application to the UK and Ireland—two countries that have much in common while displaying different levels of inequality—shows that differences in tax-benefit rules between the two countries account for over one third of the observed difference in disposable household income inequality. Demographic differences play negligible roles. The Irish tax-benefit system is more redistributive than UK’s due to a higher tax progressivity and higher average transfer rates. These are largely attributable to policy parameter differences, but also to differences in pre-tax, pre-transfer income distributions.