This chapter examines how family structure shapes patterns of poverty among workers in the United States (US) and the United Kingdom (UK). First, the authors offer a conceptual overview of the links between family structure, work and poverty. Then, using data from the Luxemburg Income Survey, they provide a statistical portrait of changes in the incidence of in-work poverty by family type over the 1994 to 2010 period. Their results show substantial gradients in in-work poverty across different family structures. With few exceptions, working households headed by single adults face considerably larger poverty risks than working households headed by married or cohabitating couples. Over most of the 1994_2010 period, the penalty for single workers was larger in the US than the UK, as were the absolute levels of in-work poverty in each marital status category. The results also show a notable, positive association between in-work poverty risk and the number of children in the household. The comparatively high rates of in-work poverty among single-parent families and those with children, especially in the US, suggest that work alone may not be an economic panacea. The rise in single-parent families suggests that work-based welfare reform may require other policy interventions that increase the economic benefits to work.