This article examines hunger and food insecurity in relation to poverty. Evidence shows that food insecurity is overwhelmingly concentrated in developing countries, even as it also exists in wealthy countries. Today, food insecurity remains widespread in large measure because extreme poverty remains widespread, and vice versa. However, the relationship between poverty and food insecurity is complex and bidirectional. This article first reviews concepts and definitions related to food security before discussing the major approaches used to measure food insecurity. It then explains why measurement matters and why it remains so challenging and proceeds by providing a historical overview of hunger and food insecurity. It also analyzes the causes of hunger and food insecurity and interventions intended to reduce hunger and food insecurity. Finally, it suggests directions for future research.