Abstract: Saliva is the first digestive fluid that food encounters during ingestion, playing a decisive role in bolus formation, texture, and flavor perception. This review, from a systematic ‘food-mouth interaction’ perspective, first elucidates that saliva is a complex colloidal system, whose unique rheological and tribological properties are synergistically determined by various components, including salivary mucins and proline-rich proteins (PRPs). Furthermore, this review systematically discusses the multiple functions of saliva during oral processing: it not only assists bolus formation and stability through wetting and colloidal interactions; but also regulates the dynamic release of flavor compounds via enzymatic reactions, non-covalent protein binding, and foam-interface interactions; and plays a key role in texture perception through the mechanisms of salivary film lubrication (smoothness) and disruption (astringency). A deep understanding of food-saliva interactions provides crucial theoretical support for scientific research and product design goals, such as developing individualized foods for specific populations (e.g., the elderly), designing dynamic sensory experiences, and enabling targeted regulation of tactile perception.