Water-in-water (W/W) emulsion is a new type of colloidal dispersion system， which has become a research focus of colloid and interface science. In this article， we review the parameters affecting the W/W emulsion formation and the properties of W/W emulsions， and summarize the typical W/W emulsions with natural macromolecules as matrix. Then， the stabilization of W/W emulsion using particles， block polymers and polyelectrolytes was introduced. Particularly， the stabilization mechanism and the parameters affecting the stabilization of W/W emulsion with particles were emphasized. The applications of W/W emulsion in the delivery of bioactives and starch digestion are also introduced. Finally， the research direction of W/W emulsions is proposed， such as the development of more food-grade systems of W/W emulsion for the food applications.