<p>Biomolecular condensates are increasingly recognized as central regulators of numerous cellular processes. The bulk rheology of condensates (e.g., viscoelasticity) balances molecular mobility with structural stability, while the interfacial properties of condensates (e.g., interfacial tension) regulate condensate growth and their interactions with other cellular structures. Here, we review the functional roles of condensate rheology and interfacial properties, as well as diseases associated with their dysregulation. By summarizing emerging methodologies and quantitative measurements of condensate viscoelasticity and interfacial tension in the literature, we highlight key regulators of condensate material properties and discuss their implications in biology.</p>