Human saliva plays a fundamental role in oral health, digestion, and speech, and its rheological properties are crucial for understanding both physiological functions and pathological conditions. Saliva is a non-Newtonian fluid whose viscosity and viscoelastic behavior depend on its composition, which includes water, electrolytes, proteins (such as mucins), and enzymes. Rheological characteristics influence lubrication, bolus formation, taste perception, and mechanical protection of oral tissues. Variations in flow rate, pH, and protein concentration can significantly alter saliva’s shear-thinning behavior and elasticity. Such changes are observed in conditions like xerostomia, Sjögren’s syndrome, and after radiotherapy. Advanced rheometric techniques, including oscillatory shear tests and capillary rheometry, have been used to characterize saliva under physiological and pathological states. Understanding the rheology of human saliva can contribute to the development of diagnostic tools, artificial saliva formulations, and targeted therapies for oral and systemic diseases.