Tissues are formed of cells that vary in their gene expression profile but associate to form an organized unit. Recent studies show that tissue organization is monitored by an evolutionary conserved process, in which cells recognize aberrant or misplaced neighboring cells and cause their removal from the tissue. These processes have been termed cell competition, intraepithelial tumor suppression or interface contractility. While the context of these processes differ, they all rely on direct cell-cell contact with the aberrant cell. Importantly, the underlying mechanism that allows cells to compare the internal status of neighboring cells is unknown. My PhD project aims to identify the mechanism of cell contact dependent recognition of cell identity.