Sustainability is often claimed as an impact in development interventions although there is rarely a shared understanding of what it means, how to design for it, and especially how to assess the likelihood that intended streams of benefits will continue. This chapter asserts that to design and later to evaluate an intervention with sustainable impacts, the intervention must deepen indigenous capabilities to manage the program, to solve problems, and to innovate. The design and implementation also must operate within environmental boundaries, not extracting resources beyond the ability to regenerate or degrading environmental services—that is, design and implementation must incorporate the primacy of the environment. A postprogram evaluation 3–10 years after a program has ended provides evidence on whether the program is likely to have sustainable impacts. A case study of an asset transfer program in Malawi highlights the criteria for evaluating sustainability: deepened capabilities and social capital, reinvestment in program activities, and the development of backward and forward linkages catalyzing growing economic opportunities.