High and rapidly rising levels of household debt can be risky. A high level of debt increases the sensitivity of households to any shock to their income or balance sheet. And during periods of financial stress, highly indebted households tend to cut their spending more than their less-indebted peers. This can amplify a downturn and helps to explain why many advanced economies since the 2008-09 crisis have had subdued recoveries. Financial institutions can suffer direct losses from lending to households, although these losses are rarely enough on their own to cause a systemic banking crisis. The sustainability of household debt can be assessed best by looking at data detailed enough to build a picture of how debt and debt servicing capacity is distributed across different types of borrowers.