Infrastructure--electricity, telecommunications, roads, water, and sanitation--are central to people's lives. Without it, they cannot make a living, stay healthy, and maintain a good quality of life. Access to basic infrastructure is also a key driver of economic development. This report lays out a framework for understanding infrastructure resilience - the ability of infrastructure systems to function and meet users' needs during and after a natural hazard. It focuses on four infrastructure systems that are essential to economic activity and people's well-being: power systems, including the generation, transmission, and distribution of electricity; water and sanitation--especially water utilities; transport systems--multiple modes such as road, rail, waterway, and airports, and multiple scales, including urban transit and rural access; and telecommunications, including telephone and Internet connections.