This special issue of Social Service Review presents original research on the determinants and consequences of economic instability, with a focus on the interplay between instability and social policy. To frame that discussion, we define economic instability as repeated changes in employment, income, or financial well-being over time, particularly changes that are not intentional, predictable, or part of upward mobility. We also present a conceptual framework for how instability occurs in multiple domains of family life and how social policy has the potential to both buffer and exacerbate instability in employment and family structure. The articles in the volume engage many of these domains, including employment and program instability, and multiple areas of social policy, including workplace regulations and childcare subsidies. They also point to paths for future research, which we summarize in the final section of this introduction. Across many areas of life, instability marks the day-today reality of low-income Americans. Unpredictable employment and work schedules (Hollister 2011; Hollister and Smith 2014; Lambert, Fugiel, and Henly 2014), fluctuating public benefits (Lambert and Henly 2013; Mills et al. 2014; Ben-Ishai 2015), changes in romantic relationships and household composition (Cherlin 2010), and unwanted housing and neighborhood churning (Desmond, Gershenson, and Kiviat 2015; Desmond and Shollenberger 2015; Desmond 2016) all too commonly mark the lives of poor Americans. Taken together, these sources of economic instability create much greater income variability for low-income families than for their high-income counterparts, and this gap in income variability has grown larger in recent years (Morris et al. 2015). Both the causes of income variability and the fluctuations in resources have been shown to affect material hardship and adult and child outcomes (e.g.