Microemulsions are thermodynamically stable, isotropic liquid mixtures of two immiscible fluids, typically oil and water, stabilized by amphiphilic surfactants. According to IUPAC definition, a microemulsion is a "dispersion made of water, oil, and surfactant(s) that is an isotropic and thermodynamically stable system with dispersed domain diameter varying approximately from 1 to 100 nm, usually 10 to 50 nm". The typical size of microemulsions is close to the experimentally observed diameter (~100nm) of long-lived bulk nanobubbles. As schematically shown in Figure , an oilin-water (O/W) microemulsion mainly contains three components: solvent (water), surfactant molecules forming the monolayer, and oil molecules that are encapsulated by the monolayer film or are in the excess phase. The whole solution is in a two-phase coexistence state (Winsor I domain in Winsor Classification): the oil-in-water (O/W) microemulsion phase coexisting with an excess oil (O) phase. Such systems exhibit an ultralow interfacial tension, and so far, the thermodynamic stability and polymorphic coexistence of microemulsions have been well explained. The similarity between nanobubbles and microemulsions can be summarized as follows: i) They are all nanoscale entities observed in experiments, with a typical size of ~100 nm; ii) Both of them are thermodynamically stable. The thermodynamic stabilization of bulk nanobubbles has been recognized through experimental observations, even though the underlying stabilization mechanism is still under debate; iii) Surfactant monolayers on their interfaces play an essential role in their stability. The idea of the existence of surfactant monolayer for bulk nanobubbles is supported by molecular simulations. Careful experiments proved that trace organic contaminants are necessary for nanobubble stabilization, and we further demonstrated that a compressed amphiphile monolayer is required for nanobubble stability at low gas supersaturation. This feature clearly resembles that of microemulsions, for which a surfactant monolayer is required for stability; iv) The vanishing interfacial tension would provide a necessary condition for stability, both for microemulsions and for bulk nanobubbles. For stable bulk nanobubbles at low gas supersaturation, the vanishing surface tension comes from the dissolution of gas bubbles, which decreases the bubble area and correspondingly decreases the surface tension until an ultralow surface tension is reached. This is similar to that of microemulsions. Microemulsion is recognized as a thermodynamically stable system, for which the extremely low (nearly zero) interfacial tension is the key for the thermodynamic stability.