Food insecurity is a leading public health challenge in the United States today. This is primarily due to the magnitude of the problem, w50 million persons are food insecure (i.e., they were uncertain of having, or unable to acquire, enough food because they had insufficient money or other resources), and the serious negative health and other outcomes associated with being food insecure. This paper defines the measure used to delineate whether a household is food insecure. The measure, the Core Food Security Module, is based on 18 questions about a household's food situation. From the responses, a household is defined as food secure, low food secure, or very low food secure, with the latter 2 categories defined as "food insecure." I next discuss the extent of food insecurity in the US across various dimensions and the key determinants of food insecurity. The key policy tool used to address food insecurity is the Supplemental Nutrition Assistance Program (SNAP; formerly known as the Food Stamp Program). During the current economic downturn, >40 million persons are enrolled in SNAP, with total benefits of >$70 billion. This makes it the largest food assistance program and the largest near-cash assistance program in the US. After defining the eligibility criteria, I review the literature, which has demonstrated the effectiveness of SNAP in addressing its key goal, namely the alleviation of food insecurity in the US. I conclude with 4 suggestions for how SNAP can maintain and even improve its effectiveness in alleviating food insecurity.