Income inequality and relative poverty among the working-age population in Japan have risen to levels above the OECD average. This trend is partially explained by labour market dualism, with an increasing proportion of non-regular workers who are paid significantly less than regular workers, as well as by other factors, including the ageing of the workforce. Social spending as a share of GDP has been expanding in the context of population ageing, although it remains below the OECD average and the proportion received by low-income households is small. Consequently, the impact of social spending on inequality and poverty is weak compared to other OECD countries and inadequate to offset the deterioration in market income. The scope for increasing social spending is constrained by the fiscal situation. Instead, reversing the upward trend in inequality and poverty requires reforms to reduce labour market dualism and better target social spending on low-income households, particularly single parents. This Working Paper relates to the 2006 OECD Economic Survey of Japan (www.oecd.org/eco/surveys/japan).