We introduce the income data of Understanding Society, the UK Household Longitudinal Study. First, we show that the data are widely used in academic and policy research. We then discuss the pros and cons of different types of data on household incomes. We go on to describe the income content of Understanding Society, emphasising key details of data collection and data processing – specifically the derivation of net household income totals. We perform a quality assessment that compares Understanding Society estimates of net household incomes to those from a reliable cross-sectional source – the Households Below Average Income series. We conclude that the Understanding Society income data are of high quality, and so are an excellent source for research on the income distribution or incomes more generally. We finish with a discussion of future directions for income data collection in the study.