This paper focuses on the issue of food waste from a retail and store operations perspective, with the aim to identify the root causes of food waste occurrence at a retail store level across different store formats and product categories. To achieve this, we first conducted case studies, including semi-structured interviews with store managers. This exploratory research involved 28 cases across dominant retail store formats (i.e., super- and hypermarkets and discount and convenience stores). The results along with secondary data research underlie a process simulation modeling approach that quantifies the impact of selected root causes of food waste by considering the dependencies between them. Finally, we conducted semi-structured interviews with 12 food waste experts to confirm findings of the case studies and simulations and to delineate the practical implications of our research and the related solutions. Our findings show that the root causes of food waste are related to undesirable customer behavior and erratic demand, inefficient store operations and replenishment policies, and elevated product (quality) requirements of both retail organizations and customers. Root causes and their impacts differ across store formats and product categories. Furthermore, the interdependencies between the root causes in the different spheres of responsibility and influence (i.e., customers, the store, and the parent organization) are evident. The paper contributes to the literature by providing detailed understanding of retail operations related to the occurrence of food waste across store formats at a product-category level and revealing pathways for preventing and reducing the occurrence of food waste at a retail store level.