This dissertation studies how participants and food retailers involved in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) respond to the incentives created by the program. WIC's fixed quantity structure, stocking requirements, and clinic visits reflect costs and benefits for participants and retailers. These structures reflect broader incentives in the provision of safety net programs through private firms as in SNAP and Medicaid. This dissertation applies current econometric methods for estimating staggered adoption designs with panel data and partial identification under selection to administrative data on WIC in different policy settings.The first essay examines how participants' use of their benefits changes if food retailers become unauthorized. US food assistance programs including WIC require that participants redeem benefits at authorized food retailers. Using a novel natural experiment in the WIC authorization of retailers, I find that a participant that loses access to an authorized retailer is less likely to participate in WIC and redeems a smaller share of their WIC benefits. These changes provide insight into the unintended consequences of food assistance program structure and how low-income individuals respond to changes in their food retail choice set. Essay two evaluates the effect of the switch to Electronic Benefit Transfer (EBT) on the authorization outcomes of WIC vendors. WIC EBT aims to reduce stigma and transaction costs for participants but may increase costs for some vendors. This paper combines novel administrative data from The Integrity Profile and the Store Tracking and Redemptions System with a new nationwide policy data on WIC EBT implementation. Using a staggered adoption difference-in-differences approach, we find the effects of the WIC EBT transition varied across different states. In sum, independent retailers are more likely to become unauthorized following WIC EBT implementation. The experience of the financial services provider contracted to implement WIC EBT by state may mediate the magnitude of the effect of EBT on vendor authorization outcomes. The third essay returns to the question of how participants in food assistance programs respond to changes in the set of authorized food retailers, in this case examining whether participants' health outcomes and program health objectives are affected by changes to the set of authorized WIC vendors. This chapter examines birthweight as a primary health outcome for WIC participants. Birthweight affects children's later life outcomes and represents WIC's mission to support the health of pregnant people, infants, and children. One challenge with observing birthweight data through WIC administrative records is that a child's birthweight is only observed in the administrative data if the parent enrolls the child in WIC at birth. This implies substantial selection into treatment. Many infants' birthweight is not observed because the infant was not enrolled in WIC at birth. To account for this selection into the sample, I estimate bounds on the local average treatment effect of a vendor DQ on birthweight using Lee (2009) bounds. The paper finds minimal effects of changes in the vendor choice set from disqualifications on birthweight measures including low birth weight (LBW) and very low birthweight (VLBW). Results show no large effect even after adjusting for gestational age - whether or not the pregnancy went to term. This evidence can be interpreted in two ways. One possibility is that vendor DQ effects on participation and benefit redemption of pregnant people are not substantial enough to cause changes in birthweight. An alternative explanation is that participation effects are may cause changes in birthweight, but that in leaving the program themselves parents also do not enroll children, meaning that the effect on birthweight cannot be detected. Each of these three papers contribute to our understanding of how economic agents involved in the food retail environment and WIC respond to the incentives created by WIC's program rules. This research demonstrates that individuals (and to some extent firms) alter their behavior in response to the incentives of the program. These incentives can oppose each other, leading to ambiguous responses by agents, particularly firms that may face constraints set by broader chain policy. Taken together, the research in this dissertation provides evidence on when policy changes and structures in safety net programs lead to unintended consequences for economic agents, demonstrating that common program designs can affect households and firms in ways that are not expected by program administration.