Background: Phase transition and phase separation as well as their tipping points are penetrating phenomena in biology and are intrinsic properties of biological systems ranging from basic molecule complexes to cells and all way up to entire ecosystems.Results: For example,phase separation has been established as a key mechanism for biological molecules such as protein or RNA to form membraneless organelles to perform complex biological functions.Phase transitions are commonly observed during cellular differentiation,and generally,there are the tipping points or critical states just before the phase transitions.And the stability of ecosystem and extinction of species are systematic manifestation of phase transitions.All phase transition and phase separation phenomena display switch-like behavior and critical transitions.Conclusion: Here we summarize the concepts regarding the epithelial-to-mesenchymal transition (EMT) as a type of phase changes and the implication of critical transitions in EMT,and discuss open questions and challenges in this fast-moving field.