This paper presents results from an on-going joint European Commission / OECD project, aimed at monitoring the direct influence of tax and benefit instruments on household incomes. The project uses and extends OECD tax-benefit models to compute a range of work incentive indicators such as marginal effective tax rates on earned income. This paper provides a methodological background describing these extensions. It also discusses the usefulness of a range of indicators such as net replacement rates and marginal effective tax rates and to what extent they can be used to quantify possible work disincentives. The approaches are illustrated using detailed tax-benefit calculations for 2001 and comparing relevant indicators across 15 EU and 8 non-EU countries. The results presented in this paper permit the identification of family circumstances where (1) financial incentives to increase work are either small or missing altogether; or (2) resources provided by social transfers may be ...