Phase separation is a common phenomenon in daily life. It's why the oil and vinegar on your salad dressing don't mix. Protein phase separation is recently discovered in biological systems and has been shown to play a critical role in a variety of biological processes. Through high-resolution cell imaging studies, we show that there are micrometer-scale structures spontaneously assembled in the cells that are composed of proteins. In shape contrast to the traditional subcellular compartment and organelles, these protein-based structures have been found to be membrane-less. As knowledge is rapidly expanding in this area, it is increasingly recognized a lot of subcellular structures are formed through protein phase separation. Not only is protein phase separation involved in normal physiological processes, but it can also be mis-used by diseases through various processes. The Guan lab has research projects supported by the National Institute of Health to discover non-canonical mechanisms of protein phase separation that underlie abnormal cell signaling that leads to cancers.