Billions of dollars continue to be provided in foreign aid each year. However, few scholarly studies have examined whether the outcomes from foreign aid interventions are sustained after donor funding has ceased. This paper examines current approaches to assessing this issue before arguing that a realist evaluation approach is ideally suited to understand why and how sustained outcomes are—or are not—achieved. It contributes to the existing literature by presenting three new frameworks to examine the sustainability of outcomes in international development as well as some Context-Mechanism-Outcome statements. Implications for governments, communities, households and donor/implementing organisations are discussed.