From serving our most basic needs to enabling our most ambitious ventures in trade and technology, infrastructure services are essential for raising and maintaining people’s quality of life. Yet millions of people, especially in low- and middle-income countries, are facing the consequences of unreliable electricity grids, inadequate water and sanitation systems, and overstrained transport networks. Natural hazards magnify the challenges faced by these fragile systems. Building on a wide range of case studies, global empirical analyses, and modeling exercises, Lifelines lays out a framework for understanding infrastructure resilience—the ability of infrastructure systems to function and meet users’ needs during and after a natural shock—and it makes an economic case for building more resilient infrastructure. Lifelines concludes by identifying five obstacles to resilient infrastructure and offering concrete recommendations and specific actions that can be taken by governments, stakeholders, and the international community to improve the quality and resilience of these essential services, and thereby contribute to more resilient and prosperous societies.