Obesity risk depends on food energy balance. Because food and beverages are acquired primarily through purchases by household members, understanding food expenditure is central to understanding food intake and obesity risk. This paper reviews three areas of the literature that explore potential influences on food expenditure and thus obesity risk: food insecurity, food environments, and food prices. This article examines these three lines of research together, reporting key results in a comparable fashion; it focuses on recent innovations in data and research design in each area; and it includes articles that have been published since the most recent reviews. While it did not prove possible to identify a single food expenditure influence that most strongly affects obesity risk, examining the three literatures jointly highlights fertile ground for future work that combines elements of each.